I would advise towards using the proper name, virtual assistant. In time you'll find this will help with organic SEO results as well as your branding. Most professional services follow this practice and we are all professionals! This of course is simply my opinion, do what is best for you and consider all advice.
I would like to clarify, I see Kathleen is advising for your Web site URL and that can serve you better if it is short and memorable. I was thinking more of your Company name, having virtual assistant in the name of your company will help define what you do and will still help with SEO when you include it as a signature in forums, blog posts and article submissions.