I run 7 speeds on my mountain bikes. I run an 8 speed trigger shifter with re-spaced cassettes, but that is a different subject. I also am using a thumb shifter for the front (2X) because of a bad left thumb.

I think a lot depends on how you are going to use the bike. I like triggers when riding on trails/single track.

If you are riding on pavement, you can use thumb shifters, and even better, a 7 speed SIS thumb shifter. The left will be friction, but most index thumb shifters are pretty bulletproof, even the cheaper new ones. Especially when compared to cheap triggers. Your only decision is whether you want to get older XT thumbies or newer cheap ones. The older XT's will cost a lot more, and good ones are tougher to find, but in a few years you may be able to sell them for what you paid.

John