Here is my list (hours played according to Steam)

TW: Attila 4,146
TW: Rome 2 3,471
TW: Shogun 2 1,514
TW: Three Kingdoms 1,154
TW: Britannia 891
TW: Napoleon 478
TW: Empire 285
TW: Rome Remastered 283
TW: Troy 238

Warhammer 2 : 1,103
Med 2 : 264
Attila : 195
Rome 2 : 192
Shogun 2: 160
Empire: 154
Napoleon: 135
Warhammer: 23

Medieval 2 is actually probably 1500+ but I played it mostly before, or without, Steam.

Yeah I think the Steam-exclusivity didn't start until Shogun 2.

And Rome 1 isn't on the list because that one I never played on Steam. Probably a couple hundred in that one as well.

But if you add all of mine up it doesn't equal either one of your top two

I have kind of an odd history with the TW series. I absolutely loved and played the original TW Shogun a lot but then I got distracted with other gaming genres for several years so I never played Rome, Medieval or Medieval II. Shogun 2 was my return to the TW franchise and I never looked back again!

You've heard this before, but my first was Rome 1, which I liked fine, even if the era wasn't all that interesting to me. But what was interesting was the blending of the tactical and the strategical. Maybe it had been done before, but Rome 1 was a landmark title in my view.

When Medieval 2 was released I jumped on it. The era was more interesting to me and the game expanded and improved upon the Rome formula. As a pre-Steam game I don't know how much time has been invested, but it's a lot. I later bought it on Steam too, and that's where the 264 hours is. I believe it's more time overall than WH2. It has to be with how much I played.

So I think the only main titles I've skipped are Med 1, Shogun 1 and Three Kingdoms.

I don't know since I played a ton of Medieval 1 and 2 and Rome 1 long before Steam, so it skews it alot and I only have data for a few of them on steam. And for those on Steam, Empire, Shogun 2, Rome 2 and Napolean didn't seem to track.
Rome 1 or Medieval 2 would probably be number 1 if I had the numbers for them with Medieval 1 not far behind. Shogun 2 should also be high up on the list as well.

It's Warhammer 2 by a landslide with around 480 hours. Never even did the main campaign, just Mortal Empires and multiplayer.
Empire with 93, which also seems odd, I thought it would be higher as I liked the setting and naval combat.
Warhammer 1 with 71 I only grabbed this on sale right before WH2 came out and when that Mortal Empires campaign came out I bailed and played nothing but.
Warhammer 3 with 47, and that 47 is too high, I should have bailed way earlier. Campaign is too tedious and too many factions are just straight broken.

Napolean, Shogun 2 and Rome 2 each have less than 20 hours according to Steam, but that can't be right. Particularly Shogun 2, which I really enjoyed and completed multiple campaigns and a couple multiplayer ones.

Based on what I've read it seems WH III's release has been just as disastrous as the original release of Rome 2.

I'd say worse. Rome 2 for me ran like crap when it first came out and had some absurdly long AI turns and loading times. WH3 for me technically runs fine, but the bugs are campaign related where units you should recruit don't, buildings don't do what they say, can't recruit units you should, objectives you've met not counting, and sometimes saves not working. That's ontop of the crappy campaign. My vote is the launch of WH3 is worse than Rome 2.

Both had a few crashes here and there, but in WH3 they only happened for me in multiplayer.

Yes, for me it's not so much things like crashes or bugs that will get squashed. In WH3's case it was the design that failed, in campaign terms anyway. I have to temper this because I haven't actually played it, but I've done my research. Release bugs get fixed by good devs. But the only fix for WH3 is Mortal Empires at this stage.

This is similar to my complaints with TW: Troy. Technically speaking it is a very solid game with virtually no crashes and no discernable bugs. The core problem with that game for me is the very poor AI programming. The AI cheats AND the AI's behavior regarding who it declares war on and who it decides to concentrate on make absolutely no sense. The bottom line is that the human player just simply needs to avoid making any alliances at all because the enemy AI ignores those allies anyway and will concentrate fully on the human controlled faction.