As always, I will be waiting till the end to pick to be safe, but since this is what I lack:
I will pretty much just be picking based on what's Agito meta! And that almost certainly means Delphi or Lathna? If Gleo is meta (I expect
one will be) I will use her to make them a 6*. Otherwise I have a looooot of Zodiark to do... I only have 1 HD1's worth of tails so far since I've been wary of wasting time on that and instead been working on Sarisse's bow. But on the other hand, once I can make a 6*, it
would be kinda silly to make more HDs, hmm.
Guess I can always just wait and finish up the remaining tails for Sarisse first, though, if not also some of the horns involved. Like I've said for Volk, Agito can really be done at your own pace so I won't really be "behind". But it would be fun to be closer to the front lines on trying stuff again, as long as I don't get too burned on investments.
Are the Halloween or Summer characters available in the Dream Summons? Someone on Reddit said the Summer ones were, but I wasnt positive.
If not, Victor is the only character that I would want thats not limited, and I already have a pretty great Wind team.
As the others said while I was typing, Summer units are actually not limited and are permanently in the gacha pool (same for Wedding and the other random alts a few individual units have), so they are in Dream Summon. I would probably still recommend Victor over those two, but they are pretty great still so maybe that depends on what your wind team is compared to your water one?
I would expect water Spirals in the next few months too, as we've discussed here recently, so you may or may not want to consider that possibility.