I'm running 33 12.5's on some 15x10's. It sticks out about an inch or so. I kinda like it. It seems that everyone prefers 15x8, I don't do too much off roading so i'm sure that they would know better than me what's best for that application. I've never had any problems with them rubbing or anything though. I guess it's up to your own preference.
I like the 15 x 8 size rim personally. I used to have the 15 x 10 rim on my other toyota with some 35 x 12.50's. I liked the way the ride was with that set up on mine. I think that it was really sterdy. I never had the 15x8 till I owned my tacoma. I like the way they look and feel so far.
Im running 15x10's with 33x12.50 Thornbirds, and they stick out about 2 inches past my flares, but thats mostly b/c of the tires. It makes my truck wide as hell, but it looks really cool. My next set of tires are gonna be Dunlop Mud Rovers which im going to put on my 15x8 wheels.
1998 SR5 Xtra Cab 4x4 2.7L 5 Speed
2.5" Cornfed Spacers
2" PA Body Lift
33 x 12.50 Thornbirds
AEM Short Ram Intake System
Sony Xplod System
I would go with 15x10's. I like the way they look. Plus you can run a higher air pressure and won't have to worry about running the center out of the tire as with a 15x8. I had some 15x8's gave them away for 20 bucks. I personally don't like the looks or the ride of a 15x8. Good Luck with what every you choose.