Depends what you want to do with it. Overall, the TM is probably the better quality gun. It will certaintly last longer without any work done on it. The JG36 may have higher FPS, but remeber FPS isn't everything. It's only one of a bunch of factors that effect how an AEG performs. A high FPS gun could still be inaccurate as hell.
You might also want to look at the Classic Army G36. The CA bodies are the best on any G36 series, and the internals are pretty damned good too (other than a spring guide, I'm running stock internals in my CA36 with more than 20,000 rounds through it). Stock CA's shoot around 315.
If you're planning on doing a lot of work on the gun, both internally or externally, go for the JG.
If you don't want to have to touch the internals for a couple of years, go with a TM.
If you're somewhere in between and want a gun with an amazing body, get a Classic Army.
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