I have a Big Agnes insulated air core and have been happy with it so far. It is not self-inflating, and has a fairly large volume, so it can be a bit of effort to blow it up, but I think it beats out a Thermarest on every other count. It is thicker, slightly more insulating, more comfortable, lighter, packs down a lot smaller, and is about the same price.

My short answer: if you have the budget, get a good inflatable pad; if not, get one of the foam pads. On occasion, you will puncture an inflatable pad, so it is probably a good idea to get a patch kit if you go on a long tour.