Here's a link to information about WP48: http://www.boxscoregeeks.com/faq
WP48 stands for Wins Produced Per 48 minutes, and is a positionally-adjusted measure of a player's per-48-minutes box-score statistics. It takes into account the team's per-48-minutes box score statistics and the average performance of other players at the same position (some guesswork is always involved because power forwards sometimes play center, shooting guards sometimes play small forward, etc). A full explanation of all the math can be found here.
I tend to not put a lot of stock into any metric that involves 'guess work,' but wins produced seems to be gaining more traction in the league as a viable statistic for measuring current and future performance. It seems very similar to the WAR (wins above replacement player) stat in Baseball that has caught on in the past few years.
Anyhow, according to that site (http://www.boxscoregeeks.com/players?di ... s_produced) Paul is far and away the best PG in the league, but Dragic is second ahead of the likes of Curry, Lowry, D-Will, Rubio, etc.
How much weight do you give the statistic? For instance it has Kendall Marshall as the 8th best PG and there are about 28 other PGs I'd take before him.