I've done all humans, all elves, saurials, all 'little people' and all freaks (dune stalker, firbolg, draconian, etc) parties.
It really didn't matter much, as every PC is unique anyway (or should be). What it did give was a real reason for them being together as a party despite their differences. A common theme to bond over.
The all elves party was my favorite, as I started them all as muticlassed royal guards all related in some way. King gave them some 'royal expeditionary' items, sweet mounts, and sent them on a grand quest.