I have a Photon II Microlight and a Leatherman Squirt P4 on my keychain (along with a mini-Fox 40 whistle and my keys) and I swear by them both.
Neither are 'the perfect tool for any job' really, but when you add the qualifier that they must be the perfect KEYCHAIN tool for the job, there are none finer.
The Arc AAA is clearly a better light, but you have very little real estate on your keychain as it is...
-John