I’m unaware of the existence of an 11g express edition.
Have a look at the following document to get information on some of the new features/enhancements on 11g:
<a href=”http://www.oracle.com/technology/products/database/oracle11g/pdf/database-11g-product-family-technical-whitepaper.pdf”>Oracle Database 11g Product Family</a> (pdf).
A major advantage of Oracle11g over 10g is a 25% performance improvement in many SQL queries without any code modifications. We have seen this in many cases when we upgraded to 11g. Oracle11g also introduced many new business analytic functions and further improved on-line database administration capabilities too. I would highly recommend 11g over 10g in a heart beat. -TechTalker