Hello,
Are there any specific features which you are especially interested in running?
The SV1(4) release has introduced several new features to the product.
However, both releases SV1(3c) and SV1(4) have gone through extensive testing to ensure stability.
Here is a link to the release notes documenting the features, limitations and caveats of each release:
http://www.cisco.com/en/US/products/ps9902/prod_release_notes_list.html
Hope this helps!
Sachin