I'm in quite the pickle. I only have two AW spirits, and I have finally managed to narrow down the Units I really want to AW for better reasons than "AW artwork looks nice"
1. Olivie. I currently have Spica, Marius and Yuyu, and field them regularly. Spica would only cost me 12 to deploy, Yuyu 13 (Both are Cr-1 I think). She is also my go-to boss killer, her skill usually buys me time to mop up other mobs till all healers can focus on her when it gets hectic. Downside: She IS rather situational, and her main selling point is her disturbing Stat ceiling. The reset would effectively kill her greatest advantage compared to Sybilla. (who I also have, but don't care to AW atm) Also: Freakishly expensive to AW.
2. Jerome. I don't have Aria, or I'd pick her. Much like olivie, he would speed things up in the beginning. Downside is: after AW he does very little beyond the +2 UP that he doesn't already do for me. Still, my lineup is very costly to deploy, and the +2 would make quite the difference.
3. Nanaly. Because: Nanaly.
4. Spica. I have Bashira, Spica and nanaly. +7% on that dps output is VERY tempting. Downside: none really.
5. Monica. As you might have guessed, I am rather short on DC, and only have level 4 skill and -1cr on Spica to show for it. Monica could help fix that issue. Downside: then again the increase is rather small. Also: I NEVER field her because I simply have better alternatives for any given situation. So basically no use beyond her passive.
6. Healers: I have All healers except for Chydis, and ain't that kick to the nuts. I love elf units

. To be quite honest, if I had her, AWing Olivie would be my pick for sure. But I have to choose from the other healers. Either Fedora or Camilla. Fedora might close the ability gap left by my lack of Feng Shui Masters, Fedoras downside: Expensive to get back up to speed.
7. Mikoto. Don't look at me like that. She is awesome. She has pretty much replaced my mages on most maps; her passive low hp instakill sounds amazing vs tough mobs; tougher tokens are also nice to assasinate mages and other fiddly mobs. But her downsides are equally massive: Expensive tokens lose quite a bit of their specific niche appeal. While she IS nice, she does not quite pack the oomph I'd get from conventional mages and is significantly more expensive than witches. She suffers the usual Hybrid drawbacks of not quite reaching the peak of the units she combines. That runs contrary to what AW represents to me. It is a way to get highly specialised units for equally specialised tasks. An allrounder strikes me as odd as first pick.