I've always just seen Chrom as a bro, myself. He's not bad to look at (Though I prefer scrawnier guys, like Henry), and his boneheadedness is amusing, but not someone I'd romance. In real life, if I was friends with Chrom, I'd be too busy making fun of/shipping him and Sumia to really get involved with him more than the bro stage XD
I think Chrom's popularity comes from being the main lord, and being pretty good looking firstly, and secondly being
myself, but I can't be sure, of course, as I don't find him that appealing. Virion and Henry are my personal favourites, both in physical appearance and personality (Though localised Virion was really what made me choose him in the end XD "Stabulous!")