No matter what species you go with, it'll always be the character that makes the difference. Subconscious communication via design is easier when you try to utilize stereotypes, but it shouldn't be a fallback for your ability to communicate character without it.
I do agree frogs are a good place to, just because they aren't visually threatening to us in any particular way.
I most recommend you make sure your character can be communicated without species, colour, clothing, that sort of thing first. Heck, if your character is a crocodile or a vulture or something and still holds up, that's an even bigger plus if you ask me; it completely separates character stereotype from unspoken characterization.