Worst:
Test Engineer for a uninterruptible power supply (UPS) company in Irvine, CA (first job out of the Navy). Horrible team chemistry, long hours, shitty pay, bad (unsafe) working conditions, and a married woman was screwing the boss, then using it to make everyone's life miserable. The third day I worked there, there was a company-wide meeting. In the mid-90's the employees gave up bonuses and payraises in order to keep their jobs. Then by the time I was there (1999) the place was booming. Several people asked when they'd be getting their raises back. About the third time it was asked, the VP of that facility got up, grabbed the microphone, and said, "If you don't like what you're making here, go to work somewhere else!"
I should have gotten up and walked out then.
Best (tie):
One I'm at now from a work/challenge/pay standpoint, and being a Reactor Operator on a fast attack submarine. Like DAT said, the pay was shitty, the hours ungodly, but man, the fun!