I would suggest a process requiring some paper and pencil. First off, what are your engine
rpms? At idle, at typical cruising speed, and at "battle speed"?
Ideally you want an alternator
that fits your engine
spaces (sometimes there's not much room) AND:
Puts out some charging
power at idle
Puts out good charging
power, full rating, at cruising speed
Won't burn out from the rpm
at maximum engine speeds
And that's all based on the ratio of the alternator pulley to the engine pulley, which will determine how many shaft rpm
the alternator is turning at. Sometimes the stock alternator pulleys just don't work
out right, and you need to drop a fast hundred bucks at a machine shop to get one that is right for you. That can literally cut your charging time in half.
Some alternators can be rated as nearly zero output until 2000rpm, and burning out if they run over 10,000 rpm, giving you a 1:5 rpm range if you accept "zero" output at idle. Others may put out rated power at 2000 rpm (allowing you to match up the pulley and get full power at idle) and tolerate 17,000 rpm all day long. So, you've got full charging power at pretty much any engine speed.
It can be a nuisance to run the numbers back and forth and try to find an alternator that really fits (physically too) but *well* worth the effort, considering the payback.
The Delco CS130D Type 100 is one good example of a robust and reasonably priced alternator.