Hello,
the function generator of the RTM is better and the sampling rate of the digital channels is better with 2.5 GS/s or even 5 GS/s (with only 8 channels). But R&S only supplies 16 clamping hooks. The ground should probably be connected differently.
Best regards
egonotto
SDS3000xHD does not include AWG in scope at all. But since OP already has SDG2000X series, those two together are more powerful albeit less compact.
It really depends on what OP does.
I agree with Nico that on R&S decoding is more streamlined. On Siglent it is fully functional, though, and you can do same work, albeit it is not as good looking.
There are also some differences in the very concept of the scope that also might be important to OP.
But I am sure OP knows most of that, having both.
I am guessing, OP would like to know what other people think, and what they might know that he does not.
I think RTM3000 is a good scope. It was even better few years ago when it had better resolution, larger touchscreen size with modern touch oriented GUI, than competition at the time.
Now it is mature product, meaning it is largely very stable. That also means that you cannot expect any further development. If anything, manufacturer might "liberate" some options for free in coming firmwares. Keysight used that strategy, but liberating options makes no difference to OP because it already has full bundle.
SDS3000xHD is very recent scope, released this year outside of China. It is part of actively developed platform.
It will grow in years to come..
If OP has some specific question I can try to answer.