A big plus in favour of TMO at the moment is that the latest version has vickers03's interior overhauls included.
See this thread for pics of vickers03's outstanding work.
http://www.subsim.com/radioroom/showthread.php?t=158706
The Japanese destroyers in TMO are quite a challenge.
You really have to plan your attack and work at your evasion.
I found it a bit too easy to evade when I tried RFB.
Then again, maybe I was just lucky, and ran into novice crews.
The IJAF planes in TMO are absolutely frikkin deadly!
Makes you real glad you have air search radar. And even then I've had some real close calls.
(And nearly sunk on one occasion running a career in the Narwahl. That sucker takes about 3 days to crash dive.
)
The environment in TMO is, in my opinion, the most beautiful out of the large mods. (Note: other opinions are available).
I know you like to play with externals off OLC, but this is still real important for immersion IMHO. Bear in mind you're gonna be spending a lot of time on the bridge, or peering through the TBT or Scope.
I can't really do a proper comparison OLC, as I have spent so much more time in TMO.
Maybe some RFB guys will drop in later and tell you about the Mod they play.