generators are fine if all's well w/ it and the regulator, it puts out enuff juice at lower RPM if everything is A1, but ya gotta watch the brushes don't get worn down and bugger the commutator and around here the pieces are scarcer and more expensive
alternators are cheeeep, specially at the wreckers, and last longer w/ less maintainence - I've got a generator on my 57 235 [w/ expensive replaced regulator], and an externally regulated alternator on the 58 283 - I've got a spare generator, but if I didn't, then when the current one goes, I'd switch to an alternator
I switched my 46 GMC [6v] to an alternator cuz I was havin trouble w/ cold starts in the winter, and the regulator was shot - the guy who modified the 12v one for me [for about the same as a new regulator woulda cost] set it up so it was generating [alternating?

] at real low rpm, and never had any starting problems after that!
Bill