I'm a huge fan of turn based combat, but I do really enjoy combat in XB2 and XB3. The issue is that the combat isn't very fun at the beginning, but gets progressively better as you progress through the game and unlock more combat systems. 2 is especially guilty of this, it takes most of the game to become good, but then becomes literally my favorite combat system of any game. It's one of those combat systems where I want the enemies to have as much HP as possible so that I can fight them for as long as possible.
The DLC's for 2 & 3 have a modified combat system that comes online much quicker, and is almost immediately fun. XB2 Torna is a good choice IMO as a title that can be played out of sequence, while offering good combat that gets going much faster than the other games.
Xenoblade 1 has the most interesting setting and best large scale story, but I feel like it falls short of the other games everywhere else. I really feel like default movement speed is too slow, or that the world desperately needs more in it. The world feels huge, and your people feel slow, and it just feels bad to go places. Combat is also slow and generally the worst of the series, but I really like the inclusion of the monado and its abilities.
1's DLC was better, but I'd still rank it below the other games.
2 is rough around the edges with controversial character design, but I loved the characters, story, and end game combat. The combat started very poor, and took most of the game to get good, but somewhere near the end it finally clicked and became my absolute favorite combat system of any game. I found myself wanting enemies to have as much HP as possible for fights to last as long as possible. I wasn't personally bothered by the "waifus", and I actually kinda enjoyed the gacha system since it was separate from any microtransactions and cores are easy to get.
2’s DLC Torna was really fun. The combat is much better starting out than 2's combat, although it doesn't quite reach the same heights either. Overall very fun though.
3 is the most polished by far, but while it's overall combat is more polished than 2's, it doesn't quite reach the same levels of or fun as two's late game combat does. I enjoyed the story most of the way through (especially chapter 5) but I thought the ending was maybe weaker than it should have been.
3’s DLC was super fun, the way that everything I did turned into skill points was super engaging. It was also great to play as Rex again after bonding with him in 2.
XCX was the first game I played in the series. The larger story has some significant issues, but the side stories are often really good. The combat is an improved version of XC1's, and I found it much more tolerable. The world is amazing, one of my favorite open worlds. The mechs are awesome. The game has insane power scaling, you'll go from dealing 6 damage with an attack to millions with a late game build, and it feels amazing. You get a real sense that you're growing exponentially, and it feels good. Movement is the best of any of the xeno games, it just feels good to run around. It makes me kinda confused why movement in the other games is so slow when they can make it feel this good. Overall a great game, just very different from the others.