Yes, the 6700 has Ev-Do which is the fastest widely available internet (Cingular is in the process of rolling out there 3G network which is slightly faster).
Honestly, I don't think you can go wrong with the 6700. The only step up from that really, is the soon to be released Cingular 8525 which runs on the Cingular 3G network mentioned above. I believe it has a slightly better camera (2 megapixel) and slightly faster internet. However, I don't think the differences will be enough to warrant leaving Sprint. If I were you, I would get the 6700.