I feel like gameplay wise, it's almost impossible to choose, but I prefer Xander because I like how he tanks everything instead of dodging most hits. I usually get unlucky with Ryoma (looking at you, 12% death) but Xander is just more reliable.
Story and character wise, I like Ryoma more because in my opinion, his design and sword is cooler. I admit that his character is pretty boring in the games, but he does show some insecurities and faults. In addition, his role in Chapter 25 in Conquest was awesome in my opinion and I'd like to point out that he supports and gives Corrin support when she needs it, unlike Xander. I love how his character is so focused on perfection and invincibility and when you see him crack and crumble, such as in Conquest and in Revelations, (spoilers) I think it's really interesting, and you get scared.
Because if it's one thing you don't want, it's a bloodthirsty Lobster Lord. Especially when he's after you.
