Either way!
Right now I'm running XTR, so I voted Shimano. But, the new Sram XO stuff is sweeeeeeetttttt!
When Gripshift first came out I didn't like it because I test rode a bike and shifted while bunny hopping a curb. Almost crashed a new bike and swore alliegence to Shimano. Lo and behold had a opportunity to get a great deal on a new bike that had Gripshift on it and swapping out wasn't an option. Tried it out, got used to it and loved it! I really like GS for microadjusting the front derailleur. Never had a problem and swore I wouldn't switch back. Guess what? Yep, next bike had XT Shifters and XTR Rear derailleur.
To me it's no big deal either way. Takes a few minutes to retrain your brain to doing it the other way. I would say that Gripshift is easier to get used to.
L8R
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger