If you like the staggered look, just do what I plan on doing. Run the same diameter front and rear, but go wider on the rear. My plan is to run 205 70 14s on the front and 245 60 14s on the rear. You can do similar with 15s. That way, you can carry one spare.
I was running 215/65R15's up front and 245/60R15's in the rear, 165/80R15 (25.3") front runner as a spare. I wrecked one of the 245's and all we had in stock at work was 235/70R15's (used them for the trip but not a fan)
I like the idea of being able to rotate them also (fronts always end up chopping)