CF10 is the latest production release version.
When I upgrades from CF9 to CF10 I did run into some issues, but all were related to custom Java classes I had added that relied on Java classes included by CF9. All of my code that was strictly ColdFusion survived the upgrade without incident, although I can't say that the same would necessarily apply in your case.
Welcome to the world of ColdFusion Amarnath88, as Cherdt states CF10 is the current version, the next version of ColdFusion, code name "Splendor" is still under development.
ColdFusion has a history of being highly backwards compatible so in my experience upgrades do tend to go smoothly, though there can be occasional issues. You can download the developer version of CF10 and start testing your app for free.
-- Pete Freitag