I agree that Steve was best choice, I would have had insisted the infusion of serum procedure be a Hyper-secret affair like no one but essential personel.. no politicians, press, etc. So the whole "bomb" fiasco doesn't happen. If I were Erskine I would have kept 2 vials in reserve somewhere safe from government reach just in case the worst should happen. And an antidote should they want to give it those who are unworthy.
Erskine would be best of the 4 choices but I doubt he would accept. Howard Stark would be a terrible choice, as would the general. My choice besides or in addition to Steve would be Peggy Charter. Which if they were able to "rendezvous" before he went into the ice & she had his kid that would be interesting. But if not she would still be a great substitute while he was in the ice. Especially since she would still be young & having out lived her Husband they could reunite upon his return to duty.