Alright, here I go, wading into the Groupset wars with no real expertise whatsoever. Except that, true to form, I once again think the concept is largely bullshit. It's foolish to think that one company does every single thing better than another, not to mention incorrect. I have tried all three now, on a variety of bikes, all three from a variety of eras, and one component has generally worked well in one groupset, whereas another from that same groupset has not. So instead of giving my entire endorsement to one or the other, I present for you a series of components that I think are great (and that you could get to work together).
Please note that most of my technical information comes from Sean "The Man" Hurley, who occasionally wrenches for Genesys. That's experience enough from me. I also get a lot of info from Dan, whom you should know already.
Starting from the front, you should get SRAM shifters. Initially I liked Dura Ace shifters better, but I'm come to love the way you can flick down with the SRAM a lot easier. Plus, you can use the brakes and shift down at the same time. That's handy. I never liked Campy shifters because I don't like the thumb shifter. We developed opposable thumbs so we could hold on to things, and I like to use mine to hold on to my handlebars.
However, you should get Dura Ace brakes. They seem to offer the best modulation, plus when you grab a handful they're as grippy as hell. I haven't tried all the variation of brakes, of course. There seem to be thousands these days, but Shimano varieties are still probably the most common. That helps when it comes time to replace some little broken bit in the middle of nowhere.
I also recommend a Dura Ace front derailleur. The Campy ones won't work with your SRAM shifters, and the SRAM ones - well, the SRAM Red one that I am still using - are as flexy as hell (though I hear that the Force ones are stiffer, perhaps because they use the force to change gears, rather than traditional methods of derailment).
If I had my way I'd currently be running a Cannondale Hollowgram crankset, but because I have a stupid non BB30 frame, I'm not. Instead I'm vouching for a 10-speed Campy crankset. They have the lowest Q-factor of any of the three big guys. Q-factor - essentially the distance between the pedals - is important. You know that bit in The Flying Scotsman where Graeme O'Bree is laying on the floor pedaling with his wife? And he points out that the natural pedaling action is one banana wide, whereas most pedals are two bananas wide? Dude was on to something.
Generally you have to run the same bottom bracket as your crankset, so do that. You don't wanna get too fancy now. Although I gotta say that the White Industries bottom brackets look the goods. If anyone wants me to test ride one, I'd happily do it. When I test ride something I get to keep it, right?
Are pedals part of the groupset? I don't know. But I like Dura Ace, again. They're steady, stable, virtually indestructible, and relatively light. I've also ridden Speedplay, but they have significant reliability issues, so I'm pretty down on them.
I have the same issues with SRAM chainrings as I do with their front derailleurs - they're flexy as hell. Apparently some SRAM sponsored pros are using the SRAM time trial chainrings to deal with this, but I'm not SRAM sponsored, so I can just switch to 10-speed Campy again. Or Dura Ace. On this one I'm not convinced there's a discernible difference between those two.
Down the back you're going to need a SRAM rear derailleur, because it's the only one that will match your SRAM shifters. But that's ok, because they offer the most consistent and immediate shifting I've experienced. Feel good about your choice, and have no regrets.
But - and here's where things get controversial - you should get a Shimano 105 cassette. The SRAM ones wear out quickly, and both the Shimano Dura Ace and Ultegra ones do likewise. For the average shunter like me that's an important consideration - definitely more important than an extra 50 grams in weight. The Campy ones are pretty good, but don't mesh with the shifters. So go with the 105.
Tying it all together should be a Campy 10-speed chain. Campy chains are the best. You know that bullshit line about Campy wearing in, not wearing out? In regards to the chain, it's almost true. It'll wear out eventually, but it'll take a fuckload longer than any of the others. Sure, it's more expensive, but it's totally worth it. You'll also encounter some skepticism about the chain's compatibility with all of those Dura Ace parts. Those skeptics are wrong. Embrace it.
And that's about it. Next review will be of gloves, I promise*.
* Non-binding promise.
** I also make no promises about the accuracy of the pictures in the links. Google images can sometimes be a little off, you know?