ofcourse Android , because it's thr latest one , and i ahve tried both the mobiles based on symbian , and android . i m having htc desire android based , it is capable for handling big applications and features where symbian is slower and some app not even work. android is very good Os for highly featured mobiles .
android, more people have androids so that makes me think the phones are better quality. my cousin has the ally, she loves it.
i don't know of any symbian phones, but the only downside of the droids are the battery lives. so you'll want an extra charger if you buy one.