I think SpySweeper is a worthy purchase for its scanning abilities, detection, etc.... But it is a bloody rip-off because you are forced to renew your subscription for updates. I mean I've seen it sold for $39.99 some places, bloody rip-off, I have no problems in paying that price for software but don't limit me with 1 year updates.
I would highly recmmend Spy Sweeper it detects much more than Spybot S&D and even AdAware, plus it also manages to locate stray registry entries and left over EXEs that others don't detect. However, there are exceptions, there are cases where even S&D managed to detect stuff, and there are cases where AdAware SE detected stuff. I would personally use all 3 I had a mother****** of a spyware on my PC a while ago it was called Spy Sheriff - Spybot S&D managed to detect and remove it and even locate some entries that the 2 others didn't find (i was surprised).