i think the question is what genre of music you will be using it for. to my way of thinking, 12s may sound better, for example, if you'll be playing metal riffs. but for most anything else, i personally prefer the sound of 10" speakers, as they seem to just be tighter and clearer.
i love the deville 4x10s, they're one of my favorite amps. they have a really versatile tone no matter what genre you happen to be playing...except maybe the aforementioned drop-tuned metal/hardcore riffs, which isn't usually a realm i delve into anyway.
and another big factor: if you're going to be playing live a lot, i've found in my own personal experiences that the more speakers you're playing through, the better your sound projects regardless of wattage. i have never liked using 2x12s or especially 1x12s live, they just don't seem to cut through the mix like a half-stack. so the 4x10 may give you a little more headroom onstage, though i have yet to have the privilege of playing through one in a live situation. like that one dude said, it might sound like an icepick to your ear in a bedroom or garage or something, but onstage you can be sure your chops will be heard without being the volume being dimed.
this was probably entirely more than you bargained for, but hopefully it was helpful.