Which one would you prefer and why? The are some kind of differences in reach and drop dimensions but are they so important for your choice?

I owned an Ergosum. I got it from competitive cyclist for a ridiculously cheap price and I knew I had to buy one. I prefer the Ergonova as it has less reach and I like the shape of the bend better. Still, I sold the Ergosum for a very nice healthy profit on craigslist. I prefer the Rotundo over all of these Ergo style bends. But if I had to choose one of those, I'd go for the Ergonova

I have used both. Ended up with the Ergonova, mainly because I could cruise comfortably in the drops and still easily reach the Campagnolo thumb shifter. Beware of the flare, though. For me it made hammering on the hoods (90 degrees in the elbows) nice and hopefully aero, but climbing standing up had to be done hands on drops. Also the Ergonova is more limited on hand positions than the Ergosum. They're few, but comfortable.

(I've left the 3T Ergonova for the Deda RHM shape now.)

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Bianchi-Campagnolo

Haven't ridden the sum but I have 3 sets of the Ergonova. Literally can't ride another bar. The nova has a wing style shape on the top with a nice flat top which makes riding on the bar tops really nice thats a major difference as well as the drop and reach issues. Other than that with shallow bars like these i ride on the drops a lot more than most of my teammates, even if i am not quite as deep when i get there.
For me a set of the new all black Ergonova team are a great bar for a new build.

Haven't ridden the sum but I have 3 sets of the Ergonova. Literally can't ride another bar. The nova has a wing style shape on the top with a nice flat top which makes riding on the bar tops really nice thats a major difference as well as the drop and reach issues. Other than that with shallow bars like these i ride on the drops a lot more than most of my teammates, even if i am not quite as deep when i get there.
For me a set of the new all black Ergonova team are a great bar for a new build. Agree with previous post if you are riding Camp the Nova works v well.

I am making a build with new sram red 2012 levers and I see many people prefer ergonova not just because of egg shape. I just wonder if most take it because of their lack of flexibility or because it is really an ideal all round racing bar.. My body is quite flexible so I would not pick a bar because of such problems as older people do.

So are ergonovas made for unflexible people or are they indeed so comfortable for daily training and racing?

Slam that stem!

I guess I am reasonably inflexible, haha.
I was using mine with 8.5 cm saddle to bar drop, bottom of bars parallel to the ground, and I spent 50% of the time in the drops. My main racing is 3-5 hours double paceline TTTs, clip ons not allowed.

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Bianchi-Campagnolo

A think to consider to is the difference in length to the drops. The ergosum is 128mm drop while the ergonova is only 123mm. This should be viewed in terms of how low you already have your stem/bars set up. If you currently have your handlebars quite low and want to keep it that way the ergonova might be better since the drop isn't as deep. Conversely, if you run with less saddle to handlebar drop than you might benefit more from lower handlebar drops *ergosum*

Basically, if your already maxed out in terms of how far you can bend while on the hoods you would want less deep drops. As opposite, if your hoods are very comfortable then a deep drop bar could give you a nice lower position just in the drops giving you the "best of both worlds"-easy comfort on the hoods yet still low and a bit more aero on the drops.

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Looks like I made a new 90 Proof friend

I origionally bought the rotundo, not what your asking about but the same length as the Ergosum. I swapped it for the Ergonova for the shorter reach (my frame is too big for me and I didn't want to run a stem under 100). I don't think you could go wrong with either product in any of their 3 trim levels. 3T makes good stuff.