Better is a very subjective term when it comes to editing and personal preferences play an important role. In any case on the Mac you have these choices:
• Buy iLife with iMovie and iDVD (Amazon, Ebay). This should be able to fulfill most needs.
• Get Adobe CS 6 with Premiere Pro and Encore DVD. Professional software with a learning curve if you come from iMovie
• Get Final Cut Pro X. Shouldn't be too difficult to learn for iMovie users but with very limited DVD authoring
Both have trial versions that you can check out. The cost for FCP X is much lower than that for CS 6.
On a side note, there is also Avid but I can't really say much about it having never used it.