I know you'll ask "does that mean the most licenses, or the best licenses, or what?" and the answer is "it means whatever you'd like it to mean!"
Include past and present (if you like). RPGs only, though, not board games.
The one true king is C7 - they do licenses well, with excellent writing, and keeping it both classy and on point.
FFG is a close second, what with their Star Wars and WFRP/WH40K licenses. They gave up the Warhammer ones... but they worked them solidly for years. Like C7, they do it well, and do it right.
West End used to be the most prolific - In their heyday: Necroscope, Star Wars, Hecules & Xena, MiB, Indianna Jones, Tank Girl, Shatterzone*, and Batman.
*not technically a license, IIUC - I think they hired Asimov to create the setting for them.
FASA had the holy grail in their day: Star Trek and Dr. Who... but it eventually bit them.
Palladium's milked one license to the point that they're more responsible for its value than the originator - as they are the ones who expanded the setting! Many people think of the RPG when they hear Robotech, not of the anime. (The Novelizations use most of Palladium's expansions to the setting, too,) I'd not call them kings, as the system is pretty wonky, but KS does do excellent setting work.
Dishonorable mention: Mongoose. Many issues with each and every licensed game. Traveller, while doing well, is not really a faithful adaptation of the game nor setting. Judge Dredd was really poor in both the d20 and Traveller versions. Glorantha/RuneQuest was meh, and was also an IP jab at Greg, essentially blackmailing him for the license. They almost F*d up their deal with ADB within the first month, too... and so Traveller PD was essentially cancelled. And Paranoia... they didn't screw the game too badly with Paranoia XP... but did violate Microsoft's IP...
