I like RTR better, but SPQR is also pretty good.

Ive noticed that RTR is much more slow paced than SPQR, in RTR you spend alot of time building and upgrading troops. In SPQR there is no build time for troops, so you can dish out troops by the hundreds in one turn provideded you have enough gold. On the battlefield SPQR normally has huge armies in the later stages of the game.

In the end RTR = Slow, less combat oriented and SPQR = fast heavy combat oriented.