What I would do first is ask if you even need any of these? Many people get them to "maintain" their Macs but many of us have been running systems for many years with no maintenance other than repairing permissions and verifying the hard drive, both done with Disk Utility. IMHO those maintenance tools are good for specific tasks such as changing hidden preferences but otherwise should be handled on a "if it ain't broke don't fix it" basis.
Personally I would stick with TinkerTool System because the developer takes great care to minimize or eliminate the sort of bugs that can kill your system. I have been using it since long ago and before OS X, and it's been a dependable tool. The many other similar tools haven't such a good record. However, I can say that Onyx, Cocktail, and some others get plenty of revisions - but that is one thing that worries me: the need. I've only used one other such tool in which I've had excellent experience - Leopard and Snow Leopard Cache Cleaner. But it is strictly a cache cleaner, and that may be why it is such a reliable tool.
Personally I prefer the one-trick pony that does what it does reliably and well. My fqvorites are TinkerTool, TinkerTool System, Snow Leopard Cache Cleaner, MacPilot or iTweaX, and Disk Warrior.
