For my Shield I also have an Alien Gear Tuck 3.0. I highly recommend you take a look at their holsters if you are looking for a double clip type. They are very adjustable, very comfortable, come with a lifetime warranty, come with a lifetime shell swap program (so if you change guns, they will swap you a new shell for free), and best of all they cost about 1/2 of what similar type holsters like the Crossbreed will cost you, but will be more adjustable.
If you are looking for a single clip holster look at the N82 Tactical holsters. I have one of these for my Walther PPQ. It is also comfortable, but tends to move around a little more for me than the Alien Gear holster. Some people also don't like the retention system with the N82 holsters, but it only take a little practice to get used to it. I'd recommend the Professional series.
If you carry all day long, I'd go with the double clip type holster. For me they are a little more stable, and don't shift as much. If you are just going to throw it on now and then, the single clip holsters are easier to put on quickly for me.