CYL3 is the easier one to pick from imo because CYL2 are getting refines soon.
For CYL3, your options are B!Camilla, B!Alm, B!Eliwood and B!Micaiah. B!Alm is good but plays too competitive a role, or infantry swordie, so I wouldn’t recommend him, due to stiff competition. Same goes for B!Eliwood, and he doesn’t really have much to offer unique to him. Lance cavalry is a bloated class with a lot of cheaper and/or better options. B!Camilla is good, but becomes mostly redundant if you pick B!Vero. If you don’t pick B!Vero then B!Camilla is a good pick. B!Micaiah however, is a good unit with nice debuffs, great minmaxed stat spread, and effectiveness. She’s going to serve you well for a long time, and even in high tier AR she’s still great.
In CYL2 your options are B!Ephraim, B!Hector, B!Vero and B!Celica. B!Eph is good, and with the new refine, he may become really really good. Axe armor however is a slightly contested role, and with other alternatives I don’t think he’s completely necessary. B!Hector is falling off currently due to how bad armors are in the meta, not that it’ll affect you much. He’s an alright choice, but still not really the best one imo. Refine could change that however. B!Celica is extremely contested as an inf swordie, and she’s sorta bad compared to a lot of them. While her refine could change things, I doubt it’s going to be so gamebreaking to the point she suddenly outclasses or even comes remotely close to the power of F!Ike, Mareeta, Larcei, Byleth and many others. B!Vero however is pretty much universally considered the best and most useful healer in the game. Her refine is just gonna make her better so that’s good. At the moment though she’s an extremely solid unit and will serve you well for ages.