What is the best upgrade path.

It all depends on your corrent running version and environment, it is often said don't fix what it isn't broken but that is not a good approach sometimes. Best thing to do is to assess your current version opened Caveats/bugs and determine whether there are critical vulnerabilities compromising your network that grants an immediate upgrade fixes, or if your current running version is somehow affecting functionality, or if there is a new feature you need introduced in the most up todate version 8.0.3 .

You will learn more in reading release notes opened and resolved caveats, I know it is tedious but is all responsability to read them.

http://www.cisco.com/en/US/products/ps6120/prod_release_notes_list.html

Is the 8.1 firmware available yet?

Only for the ASA5580

Or should we just upgrade to 8.0(3) etc..

My personal opinion I would use the latest version.

Rgds

-Jorge