Youll get allot of responses on this one If you dont have a huge stereo and amp, and extra aftermarket stuff that eats up amps , I'd most likely stick with the 50 amp. They are cheap, easy to get almost anywhere
You could go to 60 amps if you headlights tend to dim, but I wouldnt go any higher : You would just be paying much higher $$$ for something you dont need
I went with a 120,and had nothing but probs and Im running FI, elec fuel pump and stereo, but other than that, nothing else, and I blew out my voltage limiter behind the dash
So I went back to my 75 amp, Im happy, and am staying that way.
What I learned, was get only what you amps need: If you are stock, Id stay at 50, maybe 60 max
ALso, very high output amps need some work on the stock amp meter as well, so some some work would need to be done there