4L60E all the way.
Electronically controlled shifts are great, set it and forget it.
You can also modulate line pressure with a laptop, want it to shift harder punch a few keys and it's done(to an extent).
They'll take some serious HP without much for work and a lockup converter will greatly aid your mileage/trans temps.
It's really too bad Chrysler hasn't come out with something that could be easily adapted to early stuff like Ford & GM have.