It really depends on what you are happy with.
But the fact that you asking in this thread, shows that you have your doubts.
What you'd also need to consider is your location, and the kind of traffic that you will driving to the site. Is it printed (posters/cards/newspaper), via links, search engine (I'm not referring to SEO purposes), etc. If you are printing it... you might want to consider an extension that your clients would remember/are familiar with. Is .biz such an extension?
You need to consider the perception that your customer would have when seeing your url printed somewhere.
If you print the .biz on your cars or sand-blast on your office doors/ windows/etc... and later decide to change to .com or some-other extension... redoing the printing/changing the doors/glass that will be another cost to consider. And it sounds like you may have your doubts.
If you have a .biz and a .com (slightly longer), I'd choose the .com.
Any extension can be developed.
In the end-it's up to you.