My most recent hard mode playthrough was with: Ike, Zihark, Oscar, Boyd, Ilyana, Brom, Kieran, Lethe, Ranulf, Reyson, Mist, Elincia, Tanith, Nasir, and Giffca. I generally like to choose Oscar and Zihark a lot, but I found a liking for Brom. He got caps in str, ski, spd, and def on his own. It was so awesome watching him hit Luna after Luna consecutively during the same battle. I am probably going to prefer using him more often (rng blessed). :)
Oscar does great job on my playthroughs as he never lets me down or gets bad stats at the end, this goes for Zihark and Kieran too. The only real upset was Ilyana. I had to stick her behind Zihark and position her between tight choke points to make sure the enemy did not attack her while Zihark acted as a wall off. The only three characters I will continue to use are Brom, Oscar, and Zihark more.