Namek: ... Bright, very bright. I don't like bright maps, makes it hard to use the scouter.
Cell_night: I like. Good for a nice fight. Rocks to jump behind then come back out with the most powerful attack. It's petty much out in the open, however. Thus making it hard to get a few moments to ones self and transform or whatever. Also hard to see dragonballs.
Cell_day: Can see dragonballs and opponents better, but barely.
Riverside: Nice, but it's also too bright for my taste. And even less area to dodge kamehameha or whatever.
Kami: This is good for a one on one, however it lacks real content. I can rush through the pillars pretty good and I've dodged shots by doing so. Probably my favorite out of all the ones you mentioned.
Snakeway: Only tried version 2... Like Namek, I got some trouble with the scouter, and those clouds really tick me off. But it's ok, I guess. Haven't had much time to fight in it though.
Battle arena: I don't like it. Makes me queezy not being out in the open, and I worry if somebody uses genki dama or final flash.
Out of all the standard maps, I like city the most. A combination of out in the open (higher up) and good dodging area. Makes for a good heated battle.. And it's so damned cool. I keep expecting Hildegarn to come strompin through.