Yeah and while I could probably give you a relative value ranking of those champs, the real answer is that you need to pick the one which is best suited for *your* roster.
As an example, it's pretty commonly recommended to level your starter to 60 first, and so if Galek was your starter and you have no 60s yet, then I'd suggest him. But on the other hand if you already have, say, Kael at 60, then Galek has no further use for you.
I think you need to work on your CB team. It doesn't look like you have one right now, but you certainly have the team to build one. It doesn't look like you can build an unkillable team yet, so I think your best bet would be something like:
You'll want to use https://deadwoodjedi.info/cb to properly tune the team. Speeds should be between 171 and 189, with Martyr being slowest. If you're expecting to deal with green cb, you'll want to make sure to change the dropdown to spirit, so you can ensure that your speeds don't fall out of tune.
With that in mind, my suggestion would be any of those in my list who aren't at 60 yet.
I'm looking to advance a magic affinity champ to advance on the missions list.
agree with krama about the need for a cb team, but you do have the pieces for an unkillable; https://deadwoodjedi.com/speed-tunes/warmbat/
start with seeker, he'll get you your magic affinity champ.