MTX-4 is a good car out of the box, you just have to make sure you adjust your 2-speed shoes and gear mesh correctly. If there are other MTX-4 guys racing at your track, they can probably help you with any issues that may come up.

Team XRAY guys have been kicking ass with the NT1, so you know it's as good as anything else on the track. If plan your spares kit well, parts should not be an issue for you. Support wise, you just need to do your homework and learn everything you can about the car. Although the guys you race with might be running a different car than you, the concepts are all pretty much the same - so they should be able to help you a bit, but it won't be 100%.

If you are new to RC and think you'll need a lot of help, then the MTX-4 is probably the safer choice if you decided to buy a car today. If you think you can do a lot of "self help" and like a good challenge, then get NT1.

Good luck.