At present, I subscribe to neither.
In the past, I've subscribed to both. I'd be much, much more likely to subscribe to a pay web site in the future; 'news' content is always more up-to-date on the web (to the point most is irrelevant by the time a magazine hits the stands), web sites can offer things like early downloadable demos of electronic games, and web sites, especially on the pay side, inevitably have searchable archives. Subscribing to a magazine for a year means getting the next 12 issues; subscribing to a web site means getting the next 12 months of content (which almost always means more content than a magazine on a monthly basis) and also getting the entire archive of the site.
On the flip side, the production costs for a web site are dramatically less than for a magazine. Even though the web site would be as or more useful, I wouldn't pay the same price for it I would for a magazine.
IGN Insider is, I suspect, probably a better model for what Wizards is going to do that a straight-up 'e-zine:' extra content, including stuff that goes beyond what a print magazine can do, that builds off the free part of the Wizards site. Insider costs $1.66 US/month with an annual subscription, which is very reasonable (I'm not currently a subscriber because electronic gaming of the type I enjoy is entering its traditional 'new console generation dry spell').
Recognizing that IGN serves a much wider customer-base than Wizards, and that <$2 is an absolute steal anyway, I would pay probably $3-5/month for an equivalent Wizards service, especially if it meant additional content for the D&D and Star Wars miniatures games, d20 Modern and the upcoming Star Wars Saga system as well as D&D. If the d20 Modern and Star Wars content was solid and frequent, I *might* go as high as $6-7 a month, but at that point it's as or more expensive than a magazine despite costing vastly less to produce.