With my Water I like using Angela (but she is a Priest not Wit) to help in assisting. So maybe since your water is Wit just go with what you want. You want your Wit to have a damaging pet? Go with something like Niss, Fred, or Victoria. Healing pet? Angela is the usual and more popular choice.

For your RB fire go with Fred, Niss, or Victoria. Those are the usual pets I see with them. My non-RB fire is training a Sam though. Only reason is because I think Sam's a cute pet xD

For me: I just go with pets I like.