Diamond released their December 2015 comic book sales numbers, and DC Comics had a slightly better than normal month. I've tracked some of the numbers in the past, and DC usually runs around 25-26% market share while Marvel has a strong lead around 38-40% market share (significantly buoyed by their acquisition via parent Disney of the Star Wars titles). In December 2015, even against Marvel's Secret Wars and the release of Star Wars: The Force Awakens, DC Comics grabbed a 29.93% market share of units sold and a 29.32% market share of retail dollars.
Although I'd like to see better sales numbers for the Superman titles, it is really Batman and Harley Quinn that are leading the DC pack. The top book for DC was the much anticipated Dark Knight III: The Master Race, and the regular Batman title plus the crossover with IDW - Batman Teenage Mutant Ninja Turtles #1 - also appeared in the Diamond Top 5.
Harley's Little Black Book #1 was in the Top 10 and on the graphic novel side, Harley Quinn volume 2 and volume 3 both appeared in the Top 10. The graphic novel setting the stage for Batman v Superman: Dawn of Justice (March 25th, 2016) also sold well, as the Batman vs. Superman trade paperback came in as the 4th bestselling graphic novel of the month.
One way to look at these numbers is that Batman and Harley Quinn are very popular, while the rest of DC's line is down. The way I prefer to look at it, though, is that the DCYou initiative launched in the first half of 2015, with it's increased diversity and expanded creator control, is gradually reaping benefits, led of course by the popularity of Batman. I hope in the near future to see some new statistics about comic book readership, because early signs for the DCYou were positive in terms of reaching new readers, and if those demographics have remained, I think DC might be able to reach 30% market share in 2016.