check http://millenniumwaraigis.wikia.com/wiki/Story_Missions
see which maps you still havent obtained soma/daniela from. as well as urgent mission drill/strat lesson (can't remember if there's any archer from those)
if you still can't obtain the last archer, I'd suggest taking out daniela since soma already has 30% affection (unless you somehow already killed the 30%, then gg to you).
Otherwise, keep 1 copy of both would be best. eventually you'll want a cc'd soma/daniela/bashira/spica for archer lineup.
@xeare204: I personally don't suggest you cc azami. considering what you mentioned, Azami will be a very niche unit for you. her high cost makes you deploy her rather rarely, and she really isn't powerful enough under general conditions. even more so considering you will be lacking silver units early to cc plat units. better off using the silvers to cc your silvers and gold (1 silver unit vs 3 silver unit consumed during CC is a big difference). Obtaining a basic full silver/gold lineup to follow guide videos is much more important for clearing event maps early, IMO.