M!Robin or F!Robin?

I would choose based on whatever teamates s/he'll have most often. Choose based on what you need to balance out your colors.

The only reason to choose M!Robin, besides color is availability. F!Robin you'll have to spend your grails on and there are probably better units you can use them on. If anything, aside from feathers, choosing M!Robin will allow you to build two units at once, as you are saving grails for a different unit.

Male Robin is arguably better, but it depends on the team they'll be on. If the team already has a blue unit, but no greens, then Female Robin is the better choice.

F robin is a bit better than M robin if you include AR, because brainhardt + blyn.
she can take care them for you.

There are some small yet meaningful factors when deciding.

What's the team?
What Color do you need?
What are you struggling with/against?
Are you willing to spend Grails?
Do you need IVs to perform? (I know you said don't factor, but it IS a big part of it.)

Small things like this can really be the deciding factor, because the only differences between the two are they're different colors, one has access to IVs, and tbe other needs Grails, a rather rare item at the moment.