I have used all three over the past decade, and there are definite advantages/disadvantages to all. My favorite, and most comfortable, is quality leather in a Sparks VMII "style" where the belt attachments are spread out. This makes for a wider footprint and helps distribute the weight. A true, rigid, gun belt is a MUST for comfortable carry also.
High quality leather, in other words not soft suede, breaths, conforms to body, and looks great. Make sure to get one with a reinforced mouth so that it doesn't collapse too. Expect to pay more and wait more, as it takes more time and energy to craft leather. Most leather holsters, not all though, are not adjustable for ride height or cant.
My next favorite are hybrids. They are comfortable, and conform to your body, but, depending on the non-kydex material, they can collapse after drawing to make reholstering problematic. Sometimes the kydex shells, clips, or other attached parts stretch or break, and, depending on the holster maker, will not be/cannot be replaced. Many hybrids come with the metal belt attachments, and while these are sturdy, they do bend. Worse than this though is they have a little "edge" that sticks off of the holster/clip body (so you can easily grasp it and bend it out to take on/off) that wreaks havoc on clothing and chairs. The good thing about kydex holsters though, because they are usually built to adjust cant, height, etc., is that almost any kydex or leather attachments can easily replace the metal if you prefer, regardless of manufacturer.
My least favorite, but still with many advantages, are full kydex. Full kydex is the least comfortable option - it does not breath or conform to your body. If you live somewhere warm or are often hot, it will cause perspiration to build up between your body and the holster and result in discomfort. I've had a few kydex holsters, from reputable makers, break (they were all replaced, but now sit in a drawer largely unused). However, kydex is slick, thin, lightweight, and usually, when of high-quality, won't collapse (thicker kydex, which seems thinner than cowhide, has never broken for me). It's easy to draw and reholster, and is super easy to maintain (sweat and dirt is simply wiped away). I try to keep full kydex for OWB/training/competition. Kydex is often more affordable and near instant shipping. IMHO, kydex doesn't offer as much uniqueness/fine craftsmanship (although some are available with designs, and most offer different colors now) as leather (designs, materials, personalization, etc.).
That's my $.02.