Been using free version for about 5 years now. I'm a software developer so am on a PC quite a bit, for an average user as commented before, I would stick with the free version :)
I most definitely would NOT recommend the paid version. I installed it as a trial and found that all those extra features slowed my machine in exactly the same was as Norton. If you don't need the extras, install the free version. If you do need the extras, forget Zone Alarm, and have a look at Outpost Firewall Pro
Whatever you do do not bother with the paid one. What a lot of ... it is and it totally messes up your p2ps. Just like others said try the free one at least then if it doesn't work you can always change it.