My personal opinion? Write the word "and." It just seems more clean, polished, and like you weren't too lazy to spell it out. When I think of professional writing, I think of things like this.
Professionally? I think it is important to determine a writing style and to stick with it throughout the project, or across the board if you choose. I am a big fan of the Chicago Manual of Style. I generally stick to their recommendations. Join their site or buy the latest version of the manual if you are going to be doing any serious content writing.
Or choose AP style. Or any other guidelines. But, find a professional style, not something from a Wiki that is made up of users like us!
Here is a link to a quick Google of one instance of Chicago Manual's opinion...