For me, I'd have to say Old School X-COM (UFO Defense, TFTD, X-COM Apocalypse to an extent). I love them in a way that I just do not enjoy NewCOM, but the interface was quite possibly based on the recovered works of a 13th century scribe, and is very difficult to get used to for an unfamiliar player.
There are elements I like about Medieval II that aren’t present in later TW titles (like the armies not needing to be attached to generals, or the simple province system) but it hasn’t aged well in a lot of other respects. Still oh so satisfying to nail the flank of an enemy blob with cavalry or assault infantry. Plus, the Third Age mod is probably the best Lord of the Rings strategy game out there.