Raven

Just wait; He's available at 3-4* now so hunting for IVs shouldn't be a huge issue

Raven is one of the few units that does not really care all that much about IV's. Even with a +Res -Atk Raven, he could still hit 55 attack with Fury, and that's without the possibilities of Attack Tactic/buff units.

It's better to have one that's +Atk or +Spd, true, but it really isn't that much of a big deal.

You should build him now if you can spare the fodder. Even if you can't, lesser used units have Fury 2 as a budget until you get a Hinata(Assuming you are going with Fury). You can always merge them together later.