I think BigBlueToe has the right attitude -- just about every common shifting option is totally fine, and it's pretty easy to adapt from one to the other.

I happen to prefer bar-end shifters, but I wouldn't say that's based on some truly rational personal evaluation of the different options. Perhaps the first touring bike to capture my imagination had them, and that set my preference... I really don't know. But, if my bike were magically converted to brake-lever shifters, I'd be perfectly content with them as well.