What do you want your avatar to say about you? Think about how you will use your avatar and who will see it. For example, I teach online. How do I want my online students to see me?
I tend to be casual. This is fine when students know me. What about new students or prospective new clients?
The best way to determine how you want your avatar to look is to use real world analogies. I may dress casual when I teach but would I dress the same way for a teaching interview? If I use one avatar for business it is best to be a bit conservative and create an avatar that is appropriate for all business situations.
People have many facets of life. You may want to create different avatars that represent these different facets. For example, you may be a lawyer by day and a jazz musician by night. In this case, create a corporate avatar for your online legal interactions and create a more hip avatar for your music discussions.
Online business mirrors the real world. When you create an avatar, think about how people would measure that appearance in that real world environment. That will help you determine the right avatar for your online professional interactions.