Defintely the SCT. Doug904 of Bamachips.com put a SCT chip in my car and it picked up quite a bit over the entire powerband. Even cruising around, the driveability of the car became so much better.
Edit: I also noticed you wanting to buy a bottle heater, so I assume you are going to spray it. I would definitely go with a 4 bank chip like I had. That way you could have 1-2 n/a tunes and 1-2 nitrous tunes. I had it setup that way and it worked great, as you didnt have to stop and flash the ecu anytime you wanted to spray.
Here is a graph showing the before and after. Red is stock tune, blue is the SCT.