I own all 3 games and i say. RTW is the best.

Sure it has some teething problems and judging by CA's past efforts i am optimistic they will improve the game greatly with BI.

RTW has better graphics and A1.

in MTW factions just kept creating units unitil they were broke this still happens but to a lesser extent.

in MTW armies were so unbalanced it was'nt funny.
i got tired of playing against armies composed of nothin but archers.

and sure the battlefield A1 in RTW could be improved too.
like the continuos shuffling around, and the attack in
piece-meal strategy. ( try a custom battle where both armies are equal it's not as bad as many people try to make out )

But if you look at the many improvements made in the 1.2 patch, You just have to be confident that BI is going to take this game to a whole new level.