Which version? Express or Standard?

Hello,

I am trying to determine if SQL Express is suitable for our application needs.  What criteria should I apply?

I'll be installing a document management system (going paperless) and AutoCAD Vault on a VM server running WS2008R2 64 bit with plenty of RAM, HD, & CPU. 

The 10G size limitation will not be an issue with either application.  What other factors should I consider in choosing Express or Standard to run instances of production applications?

Thank you in advance,

Brian