I tried RTR for about 2 turns, and decided I didn't like it. Don't flame me, I know that I probably didn't give it enough of a chance, I just didn't like the feel, and decided to go back to vanilla. I did play Mundus Magnus, v2 for a while, and I did like that. The best thing about it IMO is that there are more territories and the cities are generally closer together. Ironically, the reason that LXPeng stated that he liked MM, was the thing that I disliked the most about it. I felt like I spent most of my time fighting rebels, which isn't bad at first, but feels kind of boring, like I'm not fighting real enemies. I like concentrating most of my efforts on exterminating a new enemy, and I felt like there is just too much buffer space between the real factions in MM. It is, however, a great mod, so you should definitely try it out. Also, don't think I'm bashing RTR, but it just wasn't for me.
At any rate, you should at the very least get the 1.2 patch (or 1.3), as those are the only official mods beside Barbarian Invasion.