Don't know if anyone is still interested since this thread has been quiet for 5 days now, but I recently joined with Zenfolio after being with pBase for three years.
Yes, pBase has excellent traffic, but there are two areas where Zenfolio beats them hands down. 1) Any questions you pose to the pBase staff goes practically unanswered, as they leave it to the forums to have questions answered. Zenfolio's staff answered my initial questions, even after I had already signed up, within one hour. 2) The pBase interface is definitely inferior to Zenfolio. In order to get your site to look just the way you like it takes some knowlege of CSS. Although I know a thing or two, it still took me a great deal of time to tweak the presentation on pBase, time that I'd rather be taking pictures rather than be behind a computer screen.
As for Smugmug, it appears to be a good alternative, but it is definitely much more expensive for the unlimited plan ($140 on Smugmug vs. $40 on Zenfolio). Hopefully Zenfolio won't raise their prices anytime soon.
Granted, some of Zenfolios features are not yet on-line, like comments and such, but I'm confident they will be available soon.
I just wanted to put this out there for those that may be considering any of these services.