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to the OP: you seem to be slightly confused about groupsets, so let me give you an engineers laymans discussion about groupsets.
Groupsets may either be mechanical, hydraulic-mechanical ( in the case of some mountain bike groupsets and some new Time trial brakes, ahem) or electronic.
mechanical- run on your standard steel cables. this technology has been around for decades and sets the bar for servicability, durability, no-nonsense. all your mentioned groupsets, except Di2, and EPS, are mechanical. note that brakes will ALWAYS be mechanical (or hydraulic.) there is no discussion. the chance of failure of an electronic brake is simply much higher than the chance of failure of a mechanical brake, and I'm sure you want your braeks to work close to 100% of the time.
how does mechanical work? well, simple. they work by something called cable pull. when you pull your brake lever, you are at the same time pulling the brake cable, which is now being stretched. ( in tension, the engineers term). because the other end is attached to one of your brake arms, this pulls your brake shut.
similarly, when you push the shift lever, the shift cable is either pulled or released (dependinf if you shift up or down). the other end of your shift cable is attached to your derailleur, and in your derailleur are springs. the spring allows the deraileur to move according to the tension in the cable, and position your derailleur where it needs to be relative to the cog/crank. the derailleur 'pushes' the chain when it moves, allowing you to shift cogs.
Different companies have different cable pull ratio- i.e. the amount of cable that is 'pulled' when you shift. shimano and sram 10-speed are pretty much the same, and hence their cassettes and to a limited extent, their shifters and derailleurs are compatible. campy is different.
How does electronic work? the brakes are the same. but electronic works by sending 'signals' when you press the shift lever.. a tiny computer processes this signal, then tells the derailleur to 'move'. a motor in the derailleur then moves the derailleur the required distance. how much to move are all determined by software that is programmed into the computer. because it doesn't run on wire tension, it 'needs' less maintenance ( although you need to charge a battery.) it also works in all conditions - e.g. shifitng under high load, which might not be so great on mechanical. do note that electirc is still widely less available ( and less well known by mechanics) than mechanical groupsets.
So, what are the differences in groupsets? well, how well a groupset works depends mainly on how well it's set up. a poorly set up Campagnolo super record EPS will be worse than a well set up tiagra groupset. this is even more stark when comparing mechanical groupsets- any kinks in the cables, smooth lubrication , etcetera will affect it. especially with internally cabled bikes. a groupset that is shifting the gears is doing the job it was designed to do, and IMO of 5 years of riding differences in 'shift quality' between any mid level groupset and up can really not be felt by a rider. braking however, is a different story- some brakes are definitely better than others, for example I feel shimano brakes have better stopping power than sram. but this is a personal preference thing. you'll have to try it out yourself. that said I have sram brakes on my race bike, they work perfectly fine.
to my knowledge, a higher price in groupset is not buying you much except weight savings, and possibly a marginal design improvement. to my knowledge, the mechanism inside each company's groupsets remaisn largely the same, with minor adjustments- i.e. the mechanism in rival is the same as sram red, they work exactly the same way. red just uses more exotic materials like carbon, titanium, etc, to save weight. the same applies to shimano and campagnolo- e.g. super record works just as well as record, you're really saving just a few grams here and there.
Do NOT assume using more exotic materials like carbon and titanium is always good for you. will it be lighter? certianly, yes. will it be more expensive? will it be superior? well, it depends. will it be more durable? probably not. previous posters have posted about shimano cranks being the best in the business despite them being aluminium, compared to campy's carbon cranks. This is true. one of the best cranks ever made, the cannondale hollowgraw SiSL, is also aluminium. Shimano is good because of a special cold-forging technique ( a manufacturing technique) that is a shimano trade secret. Aluminium , as a material, is much more predictable and consistent than carbon fiber, which is why you hear of one off cases of carbon cranks sometimes failing (rare, but it happens.) this almost never happens with aluminium. it's much more durable, can be made really stiff, resistant to damage. and shimano is able to manufacture thousands of them at the same consistently good quality. shimano chainrings are also the ebst in the business, becasue of the forging they use. everyone else in the industry (except praxis, but they're tiny) uses machining to make their chainrings, which is inherently not as good as forging. are shimano cranks good?yes they are. they are super stiff, durable, shift well, reliable, easy to service, and resistant to damage. are they slightly heavier than campy or sram cranks? yes. but that depends. shimano didn't think lightness was their main consideration in designing the crank. do you see what I'm getting at?
in some cases, such as campy or dura ace 9000, you may get more gears ( 10 versus 11) as you move up the levels of groupset. this is only temporary- eventually this technology 'trickles down' to the lower tech. most 'mordern' groupsets are at least 10 speeds.
do note you can also usually 'mix' groupsets- e.g. you can have a dura ace crank and brakes with ultegra shifters and derailleurs. this si true for most groups within the same company.
so what are the REAL differences between groupsets? well, here are some distinct differences that may help you make up your mind:
1) shifters- campagnolo shifters, for the most part are rebuildable- i.e. if some small part in the shifter fails, you can repair it, or send it off to someone who can. Sram is also rebuildable, but I do not know of anyone who offers this service. and I've tried, but you'd have to be really skilled or have a watchmakers finesse to do this. shimano shifters are not rebuildable.
also, shifter shape. each brand has their own take on the shape, and this is a personal preference. different people will like different hood shapes better.
shift lever design- each company shifts slightly differently, campy and shimano have 2 levers, sram just one shift lever. as an engineer, heres some props to shimano- they're proabably mechanically, the most reliable and sound. I've taken apart sram shifters and their inherent design leaves them much more susceptible to suffering critical damage in crashes or accidents. not so shimano. sram is lighter because of that, but is this a risk you're willing to take? I havent taken apart campag shifters before, so no comment there.
2) shift 'feel'. all groupsets shift the gears. but some feel abit more differently than others. shimano shifting is really smooth, so smooth that you may not 'know' you've shifted. sram and campy are more 'tactile' ( i.e. think manual sports car), and sram is definitely abit noisier ( I havent used the latest iteration of 2012 sram red, which is claimed to be quieter.) here it's up to you really.
3) interchangeability and availability: sram and shimano parts are by and large interchangeable ( except the rear shifter and derailleurs.) campag is not. do note that wheels for a campagnolo groupset are also not interchangeable with sram/shimano, nless you have special casettes or in rare circumstances. shimano replacement parts are the most widely available.
4) look: campagnolo certainly wins here, being the most artistically designed and beautiful to look at. but it's a personal thing. they also ahve a storied history and know how to market it well.
5) maintenance and reliability. : here it really depends on the conditions you ride in . I find shimano to be the least finicky, and sram to be the most. campag is sort of in the middle, because it doesnt need much maintenance, but it's usually a bitch to do it.
personally, for me, shimano is the most reliable, followed by campy and then sram.
6) cost. sram is the cheapest, barring other options like microshift. campag is definitely the most expensive.
7) gearing options, and compact or standard crank? or a triple? . not all options may be available for all groupses- e.g. you won't find a campag record triple crank. sram doesn't do triple cranks either, because they have WiFli. the new shimano 9000 series will eliminate the need for compact or standard cranks anyway.
so, don't sweat your shifter choice. buy what you can afford, and what you like, they all do the job well. a well set up groupset, properly serviced, is more than good enough for any protour level rider. you won't be losing a race because of it.
hope this helps you!
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