This comes up so often and there really isn't a definite answer but the good thing is you can't go far wrong!
The Mafell/Bosch track system is generally thought to be best, easier to join rails and easier to change splinter strip.
Don't think anyone has mentioned riving knives, think only Festool and DeWalt have one. Do you need a riving knife on a track saw, some say yes, some say no, my Festool has got trapped in the cut a few times even with the riving knife, don't know if it would be worse without one.
My next track saw will be cordless, either Makita or Festool as I run both battery platforms, so much easier when you are not tethered and the extractor bag (on the Festool anyway) works quite well.
I have had the Festool for about 15 years, still love it but do have a 3m track so don't have the track jointing hassle that some experience.