When writing dialogue where the character uses the words wanna, gotta, or gonna, should I write them as "want to", etc? Or should I actually write "wanna"? When I read "want to", my mind switches it to "wanna". But, if I read it out loud, I say "want to" and it sounds unnatural.
I actually think the wanna', gonna', gotta', kinda', deal is perfectly fine to write if you are trying to emphasis that the person has a distinct mannerism of using these more casual pronunciations. If not, stick to the more conventional presentation. Remember that the reader isn't you and won't necessarily bring the same dynamics to the read. The fact that you read it that way doesn't mean I will and if you write it that way you may present to me an over-emphasis you did not intend in the person's manner of speech.
your characters speech tells us a lot about them. Wanna is fine for less formal situations, want to is just as fine for other situations. The same character may use both depending who he's talking to. I have a character who thinks he's a bit gangsta who says aks instead of ask, "go head, aks me who's the mutha f******* cheese round here. I tells ya who -yo's looking rite at 'im!" and he's a 12 year old white kid!
Those are fine, but don't fall into the trap of having every character use them. I did that, and had to go and fix up a lot of the dialog. It dulls the flavor of those characters that really need the inflection.
My first question would be, what does the character think he's saying? If I say, "Want to go to the movies?" I think I'm saying "want to". If I'm joking-complaining and I say, "I don't wanna!" I think I'm saying "wanna". The two probably sound exactly the same, but the part of my brain that chooses words thinks it's saying two different things.