Sq taper is the most universal BB, UN 26 or 55 are around $20 and last a long time. Sq taper will be around as long as they make metal frames out of tubing.
CF frames allow the wizards to go wild, hence the proliferation of BB bearing/axle/spline variants. ISIS is a bit of a kluge and not recommended, all the
disadvantages and no advantages. There are several sq taper 'tapers' but Japanese is the most common. Campy differs a bit. HollowtechII will be around for
awhile and is relatively 'future proof'.