Just to prevent misinformation, they're not both fully upgradeable. Only the VSR is, the L96 AWS has some weird parts with no available upgrades.
To prevent even more misinformation, the TM L96 is fully upgradable. There are cylinders, pistons, springs, spring guides, triggers, bolt handles, receivers, inner barrels, buckings, outer barrels, endcaps, barrelspacers, loading fins, railsystems and more. Pretty much all you need. The only thing that doesn't exist is an aftermarket hopup chamber. Still, the original is good, so it isn't that much of a problem.
What is a problem however, is the smaller cylinder compared to the VSR. I personally believe it to be the limiting factor when it comes to performance of the rifle.
Having owned the TM L96 for over four years, and never had great results, the tedious disasembly is really getting to me. I'm seriosly considering switching it out.
If aesthetics are very important, I would still consider it. If you want maximum performance, I'd go for the VSR.