Need help with gear choice

Since you're the one that's going to live with it, you make the choice. Obviously you know the 3.90 is going to launch you off the line better, the 3.21 is going to be more highway friendly. Either is going to give you better acceleration than what you have now.
Here's some information for you to consider. :read2:

A 235/60-15 tire properly mounted and inflated is 26.1" high. With this as the set-up, the following is true:
3.21:1 gear, engine rpm @ 60 mph = 2480, engine rpm @ 70 mph = 2894.
3.90:1 gear, engine rpm @ 60 mph = 3013, engine rpm @ 70 mph = 3516

If you accept a 5500 rpm red line on the engine, the following is true:
3.21 gear @ 5500 rpm, vehicle speed is 133.05 mph.
3.90 gear @ 5500 rpm, vehicle speed is 109.51 mph.

Top speed data assumes no aerodynamic drag. Hope you find this useful.