I -2/-1 = 3.07
-1/+2 = 3.06
-2/-1 will give you slighty better acceleration with smaller sprockets for less rotational mass.
Probably can't notice the difference anyway. I only discovered that set up because Driven does not make a bigger sprocket than 47 for Marchesini's and I didn't even notice a difference with -1 front only so don't waste your time.
Superbike Unlimited and Riders Discount are the main places I buy my stuff from.
I'd get Driven steel sprockets. I'd only use aluminum if I was racing for money and/or trophies.
I plan on getting a Ti front sprocket just because....and I hear the wear is great. I put nearly 10,000 miles on steel sprockets with no visual wear.
The sprokets will definitely out live the chain.