Please use at least some classics. They're a point of recognition for any returning oldtimers and many will enjoy playing them again.

As far as I know the Bash was never a "best levels of the previous year" kind of event. Of course that could very well change now, it's not set in stone. But I think the event works well as a celebration of [n] years of Jazz Jackrabbit and it loses something if it's just recent levels.

Edit: my suggestions shouldn't be taken as a hint that the whole pack needs to consist of classics - new stuff is great. But the levels I mentioned are classics that I think would work well for a Bash-style event.