Consensus is the CA version is probably the best overall G36 make around, if only for the stronger body. CA had a reputation of really bad pistons (I replaced quite a few), but this may have changed in the last few years.
The "K" variant is probably the best overall version. Short enough to use indoor/CQB but long enough to get decent range outdoor. The scope is reasonably decent.
I've run with a couple of TM conversions, a G36KVSD and an MG36V and never had any issues with the TM body. When I made the conversions, no one had a "K" or full sized G36 out, only TM had the "C version.
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