Why argue about using just 10's or just 15's? USE BOTH!!!
You're not going to get everything you want to hear with one or the other. Use them in combination to cover all ground. If you really can't afford two cabinets, then get a cab with a 15 and a 10 plus a tweeter, like the SWR Triad. I have an Ampeg cab like that which kicks ass. It sits on top of my SVT 8x10 cab. But that 15-10 cab alone is great! If you're having a crisis trying to decide either way, make it easy on yourself and get something like this.
BTW, if anyone out there has an Ampeg 15-10-tweeter cab, I'll gladly take it off your hands. I need a second one.
Brian