Which support ticket (free) script is best ?

Tx.

Have a look at http://osticket.com/

Well we are in South Korea . In this country every body uses 1 to 1 forum. Strange they don't use support ticket system.
1 to 1 forum means you can see your posts and we can see our client's posts . Others can't see.
Even very big hosting companies use the same method. Not a good idea but this is a common practice in Korea. We have invested a lot of money for ticket system but just have a look at our vbulletin :)

I've had some success using the Hesk Helpdesk from phpjunkyard. You can modify it quite a bit since it's PHP based.