What is the difference between both?
When should I use Want to and when should I use Wanna?
I was wondering if there is the correct way - gramatically speaking - depending on the situation, or if this is just a matter of taste.
The correct and standard version is want to. As a general rule of thumb, always use want to.
Wanna is an example of eye dialect, which is writing things in the way to reflect how people actually pronounce them informally, for example
An' then Moses sez to Pharaoh...
instead of the standard
And then Moses says to Pharaoh...
That was a helluva thing to see
That was a hell of a thing to see
We use eye dialect only when writing extremely informally or when attempting to represent someone's direct speech.