If we exclude Sigurd and Celice, I would say Alm, then FE 3 Marth, then Leaf (as a lord), and last would be FE 1 Marth. However, Sigurd is the strongest
Edit: well, the problem I have with Celica is that she losses health when she does magic. I really dislike that about Gaiden, which is why I think she goes between FE3 Marth and Leaf in that list