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There are a bunch of threads on here about alternator quality -- and a group buy where some alternators were bench tested and didn't deliver the goods claimed.
A lot depends on what you are doing --- are you using heavy electrical loads?
Or a straightforward application.
If I were replacing mine, I would buy the largest commonly available alternator that would fit and deliver the power I need over the RPM range I intend to operate in.
There are specialized alternators for audio, welding, etc. that would drive the cost way up, but deliver commensurate performance.
One of the best "tricks" is an outboard diode / electronics package.