You are opening a pandora's box that you don't want to open! Ha ha, just kidding.
The consensus on this forum so far seems to be that Fastrack is by far superior to the MTH product. I too was in your position years ago and asked the same thing and the overwhelming answer was FASTRACK and do not go with MTH as it is unreliable unless nailed down in perfect alignment.
MTH track and Lionel track is compatible with anything from MTH, Lionel, Weaver, RMT, 3rd-Rail, etc..... You do not need to run certain trains on certain manufacturer's track. I run almost all MTH on Lionel track.
Plus the switches are bulletproof I hear and I must say so far my large layout is problem free!