IMO hamsters are a little less exciting to watch during day because they are nocturnal, they can be a little nippy if starteled when woken up, near sighted and will fall off of stuff, escape artists lol, slower so easier for small kids to handle (just talking bout syrians I dont have much experience with dwarfs).gerbils tails slip off, faster harder to catch, sleep several times a day, dont normally bite when woken, they jump high for being so small. kept in pairs or more. watch out for scent gland tumors. male gerbils have more of a scent to them. gerbils drink less so less smell. Both can be bitey but i seem to have more problems with hamsters nipping then gerbils, both have extremely sharp teeth and hurt alot when bit (obviously). hamsters like wheels and some gerbils (watch out for feet and tails getting caught (in wire wheels wrap duct tape on the outside and cover sticky part with some bedding so they dont get their feet stuck) anything else just ask

oh and gerbils seem to live longer though its about the same 2-3 years for hamsters 3-4 for gerbils though they can live longer or shorter