You guys are being pretty unfair to gripshifters. Yes, you have to throw them away when they stop working, However, the fixable problem that trigger shifters have (they get gummy and don`t release right) doesn`t occur with gripshifters as far as I`ve seen, so they just aovid that fixable problem all together. And when a trigger shifter bites the dust, it costs roughly twice as much to replace as a shot twist shifter.

Price aside, there are two definite advantages to grip shifters over triggers:
Twisters are more intuitive and easier for people just getting into the whole shifting thing to figure out.
The Sram front shifters with Microshift let you get away with things that you couldn`t do with normal indexed shifters, and work fine even if the cable stretches or they weren`t quite adjusted right.

Pinigis, whatever kind of shifter is on the bike you`re looking will work fine. Don`t let it sway your decision much. If you already have one type of shifter and want to try the other kind, go for it- you might find you like the new type better, and if you don`t, you can always switch them back.