PNET certainly not my favorite, signed up for one advert just to test, paid, got forwarded details, logged in, and everything shows 0 plus it says my contract has expired when I just bought an advert ... heh
it changes over time, or maybe i'm advancing in age
around 2003/4 PNet was easily the leader, somewhere along the line careerjunction took over and my most recent foray into the job market i found PNet has made a brilliant comeback, probably aided by careerjunction making some bad design decisions
can also vouch for LinkedIn, haven't tried the job hunt there yet, but i have been involved in my company using it extensively to recruit for our own vacancies