I like both leather and Kydex. Kydex has a lot going for it - easy, audible re-holstering, sure retention, fewer contact points on the gun (less finish wear), does not retain dirt and grit, waterproof. While I have many leather holsters, I prefer Kydex for competition, but my experience with it there has led me to consider it for everyday carry.
One of my competition guns is a GP100 Match Champion in 10 mm (only use it with .40 S&W for IDPA) and I am using (and liking) this holster...
Features Fully adjustable tension screws for custom fit and draw. Features an adjustable cant, straight drop, muzzle forward, or FBI get the fit you want. This is one of the most adaptable, versatile and easy to use tactical holsters out there. Compatible with most carry optics
www.speedbeez.com
While it is branded Speed Beez, it is made by Comp Tac. Just throwing it out there for you to consider.
One last note - should you choose to go with leather, you want to avoid holsters that are boned tightly enough to show the cylinder flutes - unless they are specifically for your 5-shooter. A 6-shot GP100's flutes are positioned differently than your .44 Spl.
Adios,
Pizza Bob