Helvetica is a modern sans-serif but it is overly-used. Personally, I find that Helvetica lacks personality but that could just be due to seeing it all over the place. Then again, I think Georgia is one of the best typefaces ever made. Certainly there are plenty of other ones you could use. I wouldn’t automatically just pick one that is most common. That’s just a no-brainer. The site will just look generic with no appeal.