Zend vs. Ioncube vs. eAccelerator

your settings should be saved by the datastore, but as always, download the XML file of your settings from the vbseocp.php to bure sure and have a back up just in case.

There's no definitive answer of which is better.
some work better than others on different systems.

The only way to know for You on YOUR box is to try both, and run some benchmark tests.

I personally run ioncube because i think its easier to work with

the test script, if it finds both to be ok, can only recommend one. i beleive it is simply a default hard-coded entry, as most public hosts tend to have more global support for zend they they do ioncube.

I converted from Zend to Ioncube a couple months ago. I was having an issue where my forum would be running along just fine, then all of a sudden it would come to a grinding halt for no apparent reason, and the only fix was restarting the server. After several twists and tweaks on the server, I was talked into trying Ioncube.

My forum not only seems to run faster than ever before, I have not had any problems since.

does the new vbseo supports other encoding than Zend? I use XCache

xcache will make your sever run faster (normally), it does not encode like zend or ioncube, vbseo will run fine on your sever more then likely. just run the test script first.

but zend optimizer is not compilable with XCache

Correct, which is why you need to use Ioncube