[Drakker]

Depends on what you want to achieve. If you plan to keep the plastic stock, definitely go TM, it's way better than the JG stock. If you plan to switch the stock, then it's a closer call. Everything is lower quality on the JG Bar10, but nothing is terribly bad. You can upgrade a Bar10 to be a good shooter and usually most parts will be drop-in replacements like on the TM unless you get a lemon.

Whether you use a TM VSR10 or JB Bar10, the initial upgrades will be the same. A 90° trigger, a 90° cylinder/piston kit (its possible to get a piston without a cylinder, but the better pistons usually come in kit), a new hop-up rubber and a new inner barrel (PDI/Laylax for best results) unless you get the TM VSR10 G-Spec, in that case the stock brass inner barrel is surprisingly good and you might not feel the need to upgrade it right away or at all (the regular TM VSR10 non-G-Spec inner barrel is some cheap aluminum crap though, so change it right away). Ideally, you can also get a new metal hop-up arm/lever to match your chosen hop-up rubber, this will prevent side spin that will develop with time at high hop-up setting for heavy BBs. On the JG, you might need to shim the hop-up arm, on the TM they usually fit perfectly.

That's pretty much it. Upgrading a VSR10 is easy and its mostly a settled science. You will find all kind of other parts, and people swearing about that or that upgrade part on facebook/reddit, but feel free to ignore them. You don't need all that crap in your rifle.