You've probably noticed that I almost exclusively use genuine BRIO track. There are some exceptions to this of course: I point out that you should consider getting the Maxim 3" Mini Straight or the Jesse's Toy Box 3" Straight as a substitute for the discontinued and short-lived BRIO A3 track, and there are other pieces in the BRIO system that are simply very difficult to find but very handy such as as the F2 and G2 parallel switch tracks. But by and large, I stick with the BRIO brand.
Why is that? I'll admit that part of it is that I am a BRIO purist. Virtually my entire collection is BRIO with only a handful of track pieces coming from other manufacturers. That's a snobbish reason, sure, but it's not the reason why I stick with BRIO track. So what is? Well, the mainly it is because I started with BRIO track, and the issue with mixing and matching track is that you create problems with symmetry.
Each track manufacturer uses a slightly different standard for their track lengths. BRIO's track lengths are measured in metric and their primary lengths are the 216mm and 144mm straight. The track for Thomas and Friends is based on Imperial measurements and their straight lengths are measured in inches. Maxim's track measurements are stated in inches but the measurements are actually in metric and the imperial distance is a rounded measurement, e.g. their 3" straight track actually measures 82mm which is just shy of 3-1/4". When you arbitrarily mix track from different sources, you introduce uneven lengths or curve radii into your layout, making it more difficult to create a symmetrical design.
Symmetry is your friend because it guarantees a perfect fit when your track is laid out. You can create more complex layouts from two or more simple, symmetrical designs simply by overlapping them or joining them at one end. Symmetry is really the basis for success in the wooden railway system which is plagued with 45-degree angles and other confounding geometry. Anything that breaks track symmetry serves only to introduce additional frustration into your planning.
That doesn't mean you need to go out and buy only BRIO-branded track like I do, but it does mean that you should mostly stick to a brand that you like, be mindful of what happens when you introduce track from different sources into your toy chest, and most importantly store that track separately so that you know which track is which when building your layouts.