I mean, my favorite size is like the pretty fat range, like just broke into or just under the ssbbw/bhm range, so ideally they’re all that size lol.

But putting some thought into it, going by after their game is over…
Normal size: Sigurd, Seliph, Leif, Eliwood, Lyn, Ephraim, Ike, Dimitri
Fat: Marth, Roy, Hector, Eirika, Micaiah, Claude
Very fat: Alm, Celica Robin, Corrin, Byleth, Edelgard
Huge: Chrom, Alear

Those in normal size are just who I don’t really see gaining weight. Hopefully I didn’t miss a lord lol