Welcome to the forum.
First off, all 3 guitars are very different. Because the Jag and Mustang are short scale you really need to try them before you consider buying, the 'feel' is quite different to a standard scale guitar. Sonically there is'nt huge differences, but Strats sound more 'snappy' where as the Jag lacks a lot of sustain, the Mustang is somewhere inbetween.
Whilst i like Stratocasters the volume knob position irritates me and gets in the way when i play, i prefer the knobs out of the way like on the Jag and 'Stang. The fact they are common also puts me off, i like stuff with a bit more mystique and weird shapes.
Jag or Mustang? Hmm, i love the Jag, but the Mustang is a very comfortable guitar. Its light in weight and possibly my favourate neck of all the Fenders. But the Jag tremolo is better imo, it also offers more sounds and its the coolest looking guitar ever made.
Traditional Jags take more setting up though, possibly more so than most guitars. So if you are not used to tinkering around with guitars i would avoid the CIJ vintage reissues and consider a MIM Classic Player.
It may be worth you browsing through the picture threads in each forum. 😉