You should be able to choose the kind of familiar you can get when casting the spell. It's a ritual spell that you can cast and then un-prepare, so I think there's literally no downside to taking it. The Crow is quite helpful in combat.
I don't know the exact deal with the frog myself. I made the mistake of talking to it before handling the hag, and the damn frog nearly TPK'd me! Apparently it becomes a lot calmer if you talk to it after dealing with the hag.
You should
absolutely speak with every animal that you can find. It's the most amazing addition to the game. You don't necessarily have to learn and cast the spell either, there are multiple ways to get it:
- Potions of Speak to Animals are plenty, so you can always use those
- Karlach can learn Speak With Animals for free if you give her the Beastheart (I think that's the name? It's the un-problematised Totem subclass) subclass
- Wyll can learn Speak With Animals as an invocation
So really, too many options to learn the spell. And it really gives so much more content.