Back in the day when there was only PKZip & WinZip I used WinZip, I later switched to WinRAR, then to ZipGenius, then to 7-Zip, and I currently use IZArc.
Here are my experiences with each application:
WinZip
With WinZip my biggest problem was always that it didnt support many other compression formats. For anyone who uses the internet a great deal this can be a problem.
WinRAR
My only complaint about this application is that it's nag screen was extremely annoying.
ZipGenius
Very similar to WinRAR in that it has nearly all the same features, its major downfall is that it can be very unstable.
7-Zip
7-Zip seems to be slightly slower than some of the other apps. In the past I also found that it was lacking in the features department.
IZArc
I've found IZArc to be extremely stable, fast, efficent, creats small archives, etc... However it lacks one major feature... The ability to create split archives...
This is a very simple poll really... I am curious as to what zip applications everyone uses & what their experiences with each are.