I'll echo what most here said. You win with either.
I'll also address a few things I didn't see answers for.
You said you like the a7, was my fav rda before getting the REO Grand and RM2. In the Reo sub forum there was discussion of issues using an a7 with the REO, so I got the RM2. No regrets there. RM2 performs better imho then the a7, and gives you a bit more room to work.
You can still use cartos on the REO if you choose to, they work with the bottom feed just fine. LR are probably a better bet. I've never been a carto fan, so better to defer to Bad or that cats input on how well they work.
Seen a mention of RDAs needing more maintenance, while true to some extent, my last coil/wick setup (0.8ohm flat kanthal + 2mm silica wick) lasted me 6.5 weeks. So don't really consider needing to wrap a new coil every month or two as much in the way of fiddly.
I think they corrected the problem with the A7, I've been using my fairly recently purchased A7 on my REO the whole day without issues (the positive post doesn't wobble)
Love the RM2, but I felt like vaping with vertical SS Mesh today so gave the a7 a revisit