If you’ve used the current road and tri groups from Shimano, Sram and Campagnolo, then you may have your own reasons for picking a favorite.  I have a favorite and a relatively simple reason for it.

The primary differences between the three manufacturers’ road groups are with respect to price, durability, hood shape and shifting. 

Price: Shimano and Sram are roughly equivalent while Campagnolo is far more expensive.  If you prefer carbon parts to aluminum, then Sram is the best bang for the buck.

Durability: No one beats Shimano in this category.  I think you could build a bike with Dura Ace 10 speed and it would last as long as you’re willing to ride it.  I would rate Sram ahead of Campagnolo particularly if you’re a heavy sweater.  My Record rear derailleur and front chain rings have not survived the miles near as well as the same parts from Sram and Shimano.

Hood Shape:  With respect to the shape of the hoods, I am sure that your weight and the shape and size of your hands make a difference.  Nevertheless, I strongly prefer the shape of Campagnolo hoods to both Sram and Shimano.  Between the other two I prefer Sram to Shimano.  This is a critical issue when it comes to long-term comfort and is one of the reasons I prefer Campagnolo. 

Shifting:  While all three groups shift differently, they all do an excellent job of smoothly and quickly changing gears.  I think that once you become accustomed to the particular shifting pattern, thay are all equally intuitive and the difference in my preferences are only slight.  I could be happy with any of them, but if forced to pick, this is how I would evaluate them.  Even though Sram is the newest design, I like it the least.  I particularly don’t like swinging the levers as far as Sram requires on such a regular basis.  I love the way Shimano shifts, particularly the way you can simply twist your wrist to shift with the outside levers.  Campagnolo’s thumb shifters take a little getting used to but once you do, it’s as easy and as intuitive to use as Shimano and Sram.  Overall, though, I prefer Campagnolo for the following reasons: (1) you can easily shift multiple gears in both directions with the rear shifter; and (2) you can either swing both levers all the way or push both thumb shifters all the way down to go from either the big or small chain ring and stay in the same effective gear.  In other words, if you are in a 53/17 and want to move to your 39 front chain ring because you’re going uphill, you can quickly and easily shift to your 39/14 in one fell swoop and never alter your cadence.  Moreover, you can do the exact opposite shift, from the 39/14 to the 53/17, when going downhill.  Importantly, both hands do the exact same shift to accomplish this particular gearing change.  If you’re moving to the big chain ring, both hands swing the shift levers that are positioned just behind the brake levers.  To move to the small front chain ring, both hands push the thumb levers all the way down.  It’s simple and very quick - once you get the hang of it you will never again stumble in a pace line when shifting between the front chain rings in preparation for either going up or down hill. 

When it comes to triathlon bikes, the differences between shifting and ergonomics are virtually eliminated since you don’t have hoods and all brands use very similar bar-end shifters.  There is one significant difference – the Campy shifter for the rear derailleur includes an adjustable cable stop.  This allows you to make minor shifting adjustments on the fly – you don’t even have to leave the aero position. While I rarely have shifting problems in a race, this little adjuster could be your best friend if you do.  One ¼ turn adjustment during a race could prevent hours of frustration when your chain starts skipping up and down between two gears on your cassette.

Overall, all three brands offer excellent performance and quality. The best performance for the dollar is Shimano Dura Ace.  Sram offers outstanding performance, lots of carbon parts and ceramic bearings and a very competitive price.  Campagnolo Record, though, has gorgeous looks, precise and snappy shifting, the best hoods for road bikes and performance advantages that are just enough to put it in the top spot despite its exhorbitant price.