DP has a good community spirit. We all know who each other are. Sitepoint seems to more hard discussion on webmaster issues and lacks the fun and jokes. Thats just the impression I get. However sitepoint marketplace is quite incredible. The money I have gained from selling there rather than DP is amazing. Listing a site for sale there also brings hundreds of visitors, so shows its popularity.
That's funny, people on both sides say the same -- "I'm here for community, there for sales". For me, this place reminds me a backyard where kids gather together to play, trade things, talk stuff and just fool around. While SitePoint is a well organized place that has this corporate feel to it. And it's not true there's lack of fun or jokes, simply things are in their places. That's what impression I get, but prove me wrong and tell me why I should hang around here more than there?
In my opinion I think Digitalpoint is more popular due to the fact that it has a good community but I like Sitepoint better.