Well, the time is coming for me to replace my weathered shifters/rear derailleur from last season and start looking to next season for what to ride. I'm taking old 105 off the bike, and am looking at either SRAM Rival or Ultegra 6700 to replace it with. Looking on ebay, the price difference for shifters/rear derailleur is only $50 or so, so pretty comparable.
Mainly, I care about shifter ergonomics, and both are a step up from the bulbous hoods of 105 in my world. The Ultegra has a flat ramp now and goes a bit longer for more hand positions, but from what I've read has more bits in the shifter exposed for mud/dirt/sand/water to get in there.
SRAM shifters look similar though a little shorter, but seem to be really well-respected in the cross world after they grinded out a few kinks in the front derailleur shifting from a few years back.
So, if you had the choice, which would you go for?