I actually just installed RTR 6.0 Gold (newest) the other night and am just about to start up a campaign using it.

However, I switch around...sometimes vanilla 1.5, sometimes BI 1.6, and sometimes RTR.

I play all 3...however, and you can go to the bank on this, once RTR 7.0 using BI 1.6 comes out (not that much longer I hear...couple months) that's probably all I will play...that's the combination of all three, and right up my alley