WELCOME ABOARD!
I'm certainly no expert, but people say that RFB makes it more realistic, while TMO makes it harder. I'm sure that's an oversimplification, because TMO has a very large number of hardcore adherents. One thing to watch for is the aircraft, because they can quite a ways underwater.
One option is MultiSH4 and running both, at least until you decide which you prefer. And don't forget the RSRD campaign.