I voted for another Rome, that would be great. Anything from the 19th century and the far east would be welcome too.
A WWI or WWII one would not work for the TW series. The battles of WWI/WWII lasted for months and had fronts that stretched for miles. tactical decision making was up to batallion/company level officers. Trench warfare bogged down any attack, while reserves moving quickly on railways sealed up any breakthroughs that happened.
Take the worst citadel assault ever, give every enemy soldier a repeating rifle, lots of artillery, machine guns, indestructible walls, and unlimited reinforcements, and you have trench warfare. Also, at last count there were 1673 RTS games based around WWI and WWII. We don't need another one.
For the pick 'em I chose The Persian Empire, and Caveman TW.
It is not enough that I succeed, but my enemies must fail.
I came, I saw, and was crushed.
Mongols? Time for a strategic retreat to the Atlantic.