I'm a medic and have used a Quark 123^2 neutral tactical with a recessed tail switch for a long time. It clips in my pants pocket reliably and has 2 programmable modes. I have mine set for turbo/low. I have dropped it many times, it looks like it's been through a war, but has never failed me.
The Quark Turbo looks nice for a belt, but the wider head may be uncomfortable clipped in a pants pocket. I'm thinking of getting one in a warm tint because it just looks like a great light.
I recently got an IluminaTi CA1 that runs on a AAA battery. It is amazing. It is smaller than the Preon, clips in my front pocket and looks like a pen is clipped in there. It is perfect for pupils on low, and is 115 lumens on high. It is very floody and is perfect indoors. If you leave the head twisted off, but close to the on position, you can cycle through the modes and leave it on momentarily at will by just squeezing it. Really cool.
Both lights can tail stand and can provide adequate lighting via ceiling bounce for those calls where the light switches don't work and everyone needs both hands.
For outside I still grab my Quark. If I could only buy one it would be the Quark as it is better outdoors, has a much longer run time, and is more stable tail standing if the surface it is on is bumped.
My IluminaTi is new, so I can't say how durable it is, but it is titanium and feels very sturdy. The Quark and I have a history, it is like a rock and I feel like I would be cheating on it if I got one of the newer ones with the newer LEDs.
BTW, whenever some co-worker goes to the store and gets a big Maglight LED or some other store brand that fits on their whacker belt I pull out my Quark that fits comfortably and almost flush in my pocket. It is always twice as bright as what they have. One guy had a Gladius-type light and the Quark still blew it out of the water, and with a better tint. They point out their light was only $15, and I dare them to drop it on the cement with mine and point out how they flinch.