Best historical mod for RTW?

[Marcus Hortensius Castus]

EB is good if you have a fast(ish) PC. The scripts can add a lot to the game, but also slow the game down to a crawl. It took me over 30 minutes to get into EB the first time I played it.

Depending on the time frame, RTR Ancient Empires: Elysium is great for early Republic. Roma Surrectum is great for the legions (35 named legions, 30 in RS2 coming this year sometime), has great unit variety and with a '0' turn recruitment option you can play the game with as many epic battles as you want-and, if a smart commander, as few if you block the passes right. It allows you to choose your primary area of conquest, and so on, with a map large enough to avoid total domination right away. It can however lead to superpowers in a struggle against each other later in the campaign.

Troy Total War is good for the 1200 BC timeframe, even though many units seem to be taken from the movie in the Greco-Troy arena. I've not played the Hittites or other cultures, so it's more 'fun' than 'historically accurate' imho.

For BI, IBFD is great and has a ton of submods and elective options and scripts that add greatly.