Which BB 727 is better?

The 75 has a couple advantages. They have a 1" wide front clutch carrier bushing vs. 1/2" wide on a pre 70 unit. I like the stability of the wider bushing. It will also have a part throttle kickdown VB which may or may not be anything you care about.

OOPS... Just noticed your last post so I guess my post is a moot point. You might want to consider swapping the front clutch carrier and reaction shaft/pump for a 71 and up unit to gain the wider front bushing.