Back to topic: I don't have lot of expertise in the 3 brands, but I´m not so biased as I don't care which one is better. There are only 3, and each has its good and bad points. I think there is not, "the best", at least not today, not as a full groupset. Sram has the best front shifting now. Very recently they were the worst. Shimano has the best electronic group by far. Campy is lighter than shimano, the best looking perhaps, although too classic. Sram offers BB30, although there are 3rd party cranks which are better than these three, just like it happens with wheels and brakes.
To each their own. But some people here seem to be biased, or lacking knowledge or out of topic.
Biased or lacking knowledge? Not really, I deal with Campagnolo, Shimano & Sram on a daily basis. I see their warranty rates firsthand, again day in day out. I have owned all three manufacturers' kit in the last 5 years and regularly ride the latest products as part of my job.
All three produce good stuff, but opinions on whose shifts better are purely subjective. It depends on who set up the bike in the first place too. I've worked with mechanics who can set up Campag & Shimano with their eyes shut, yet they find Sram awkward. Conversely, I know people who find things the other way round.
Sram are by necessity followers in many respects. They had to wait for Shimano to go to 11 speed so they could marry their 11 speed set up to Shimano.
From a warranty point of view, Sram & Shimano trail Campagnolo in my experience. Equally when it comes to serviceability, Campagnolo is streets ahead in its price and ease of repair. If you compare the cost of repairing a Shimano STI with that of an Ergopower it's evident that Shimano aren't in the business of serviceable componentry. Sram aren't as bad, but it is hard to find the correct parts in the UK as the distributor's website is steam powered! Campagnolo is easy in comparison. Part numbers are simple to find, and parts are readily accessible, even for models several years old.
good for you
It depends on each rider of course. But I´ve never ever broke a shimano part or sram, specially not during the warranty period, so that data in my case doesn't matter, same with reparability. Sram shifters are definitely weaker in this sense, but for a normal user, it makes no difference. weight and price makes a diference from first moment, same as front trimming. EPS is just worse from day one, also in price. And that is why it doesn't sell. Campy is definitely exclusive in price. And getting a campy wheel is more complicated that getting a shimano wheel. Also in races. Same thing happens with pedals in amateur races, talking bout second bike or car bikes.
Being a follower is the only way to use the same standards, and no new ones. Shimano can create a new standard for BB tomorrow if they want, sram just can't. Campy could, and it would be their death. No frame manufacturer would follow. Again, not the bees knees, they are ducati, for the good and for the bad.