As far as tuners are concerned, SCT is pretty much a given. They did, however just release a new one; X4 rather than X3. It has better data logging capabilities, but it won't affect the tune at all.
Most major email tune providers -- Brenspeed, Bama, BBR, etc. -- are going to be pretty comparable. Dyno tuning is where you really make your money. I'd pick whoever you have a good relationship with, if you've had past business dealings, and who provides the best support for trouble shooting and future tunes. I have Brenspeed and am quite happy, but you shouldn't have a problem with Bama.
As far as gains, they're vastly different based on the modifications done to the engine. It just depends on how much your factory intake is limiting breathability. A good intake and tuner on a stock engine should net you a solid 10-15 rwhp. Possibly more, but not guaranteed. Generally speaking, "race" versions of intakes with give you better gains because the mass air flow housing has a larger diameter. I use the C&L Racer intake, which I like because it's simple, affordable, and has a 95 mm MAF housing. The JLT Gen 3 CAI is also excellent and uses an even larger 110 mm housing. One last thing; aluminum intakes might look cool but they resist heat soak much less than composite or plastic intakes. The cooler your air intake is, the better power you'll make.
