Well, I have a Rintec, so it may be biased for me to say that a Rintec is what I would chose any day, and what I think is a good choice for most anyone. I love the way it shoots-smoothly, quietly, and easily. I have the Cam1/2-it comes on all Rintec's, and its pretty much the best cam out there IMO.
I haven't ever shot a Mustang, though, so I can't say which is better from experience.