If you're not sure which will work best for you then you probably do not know what your demands are. You need to assess what your electrical needs are to be sure of what you need. Generally the difference between a $90 and $300 alternator are not only the quality of the components but also the amp output.
I have Mechman alternator that outputs more than a stock alternator and cost a lot more as well. That's because my demands are much higher electrically (high output stereo, alarm, camera, etc.). The stock alternator was not outputting enough at idle so I had to go with a much better and more expensive alternator. It was a worthy investment it as it met all my electrical needs.
Are you considering a more expensive alternator because the stock one does not provide enough output at idle? If your electrical needs are stock then you may have a bad alternator and just need a quality stock alternator replacement. I'd suggest having your electrical system checked especially under high load to see if you need a higher outputting alternator. Hope this helps.
