Hi there!  ^_^



The OVA (or also called OAV's) were released AFTER the
tv series ended.  The OVA were only released on video.
The story pretty much continues with the TV series
ended.



The general opinion is that the TV series was better.  
(although I know some ppl who LOVED the OVA, right Ryouko? ;)
The characters are drawn a little differently in the OVA's:

In OVA II, the clothes the Seishi wore are different
Some of the characters are well.... in different 'forms' (trying not to spoil you)

I have some OVA and TV series FY cels on my page if you want to see
some differences.  
There are also a bunch of other FY cel sites on 
the Internet GUide to cels which 
have cels from both series.




Take care,


~jINx