I use 4 different OSes. They all have their strengths and weaknesses.
OSX: Tiger runs well on my G4 and G5. It seems more immune to attack-ware. It often seems there is only one way to do things. This OS seems to take the opinion that it knows (better than me!) whats best. I trust this OS the least, I wonder that the contents of my HD are reported back to Apple.
XP: It has the better thought-out UI compared to OSX. Things are hidden from me, the HD is in use for no apparent reason. I don't trust this OS either. As time goes by, it gets slower. Mal-ware? Fragmentation? Seems undefendable.
Ubuntu: Just starting to try this out. Some people wrote this OS to prove to themselves they are intellllligent! I like open source.
AmigaOS: Fun. Does what I want it to. I trust this OS, it doesn't spy on the user. Nothing seems hidden. The HD is active only when I tell it to be.
