Each one has their spot. I like M105 because I can use it with a DA polisher and it finishes down a lot better than Powergloss. Although when you are dealing with rock hard clear coat, Powergloss does a good job.
Powergloss can't finish down to what M105 can do, in my opinion.
With Powergloss I'm usually at a 3 step process to remove the extra marring caused...as with M105, I can go straight to M205 and finish there if I want...or continue to Jewel.
Powergloss is great at removing wetsanding, and M105 does an O.K. job with it, all in my experiences.