I can't speak for RS, having never played it, but IMO EB 1 (with RS environments
) certainly is one of the best RTW mods. It has a lot of great-looking units (irrespective of historicity), interesting reforms, and is very immersive and atmospheric (minus the CAI idiocy). It's hard to find another mod that compares in sheer scope (except EB 2 of course). Also, AFAIK it's still the, or one of the, most historically accurate RTW mods, relatively speaking.
That's not to say there aren't other interesting ones. My personal RTW favourite is Fourth Age Total War 3.3, which is certainly one of the most unique ones, going further than EB 1 when it comes to getting the most out of various mechanics, tech trees, and even diplomacy.