I don’t have experience with other filters; I have been using the Jnet for the past few years. I currently have level 5 filtering with shopping (if I recall correctly, regular level 5 doesn’t let you into websites such as Amazon). If you only want specific websites and nothing else, consider the whitepages system, also offered by the Jnet, in which you only get the websites you specify – if I understand correctly.
see http://www.thejnet.com for more info