Most of these lights have been reviewed by people like selfbuilt who do reviews that are much better technically then I have the facilities to do. So I'm going to focus on the more subjective stuff that's hard to get a feel for from the numbers alone.
Build/form factor:
All these lights are what I would consider top notch quality wise. In another thread I mentioned that with lights as good as the C2H and the EX10 in the $60-$70 range and the extreme for just a bit more, the Novatac better be perfect for $160, that pretty much sums up how I feel about the general build quality of these lights. That said there are some pro-cons when it comes to carrying them.
EX10:
This light is the most compact of the bunch and yet it's off my carry list for now. Simply because after getting the EXtreme and the C2H I refuse to pocket anything that doesn't have a clip. If I put the EX10 in with my phone it scratches my phone, if I put it in with my keys it gets scratched. This is the only real downside and a minor one as 4sevens should have clips for sale soon.
Extreme:
This light feel really well built and it's big head equals ample heat sinking and surface area. The checkering and anodizing are first rate and the SS bezel really makes the light look sharp in my opinion. The clip is sturdy and holds the light well making it much more practical for my to carry then a clip-less EX10. The only downside is that it's a little bulky when carried in the front pocket of jeans compared to the C2H. This makes reaching for my phone a little bit more difficult.
C2H:
This light is really hardly any bigger then the EX10 and the excellent clip makes it my favorite light to pocket carry. The lack of rough checkering also means it does scratch up other stuff in my pocket, like my hand when reaching for my phone. I haven't had any problems keeping a hold of it because depending on how you hold it you can get a grip on the leading edge of the clip of the cooling fins on the head.
The other thing I really impressed by is the fact that the pill threads into the head rather then just dropping in like the EX10. This greatly improves the surface areas between the pill and the head and insures solid contact making for good heat transfer between the pill and the lights body. This is important because the light is driven hard and gets warm quick. Although I must point out that it's my opinion that the main reason the light gets warm in your hand is the excellent heat transfer, so this is a good thing.
Beam Quality/Output/Run time:
EX10:
The beam on the EX10 is it's weakest point IMO. Mine always had a dark ring around the hot spot, at least now with the smooth reflector is throws pretty well for a small light with decent run time. As can be seen in the pics above the Extreme and the C2H are significantly brighter then the EX10, but this is made up for the fact that the EX10 has quite good run time as selfbuilts reviews have shown.
Extreme:
The beam quality is one of the strong points on this light IMO. The larger, textured reflector puts out a beam with good throw and greatly minimized cree rings. The only light I have with a smoother beam is my L2D with the heavily orange peeled reflector, and that light really sacrifices throw to be that smooth. Run time is not as good as the EX10, clearly, but it's pretty good considering the output.
C2H:
This thing is a rocket. Not only does it put out more lux at longer distances then the Extreme (see the palm tree shots) it has a much larger hot spot. The beam is quite ringy, like the EX10 or any other cree light with a similar size reflector, but the large and powerful hot spot makes the light great for any sort of distance. You pay the price for this power though, I don't have the equipment to do run times, but using high too much will run through batteries pretty quick, but that's what the lower modes are for.
UI:
EX10:
I love the smart PD idea, I just wish it had quicker access to high. Give me that and the smart ramping from the D20 and it'll be my clear favorite. One part I really like is that in momentary mode it's impossible to lock it on, whic means you can rest assured it's not going to get stuck on (unless it gets wedge in such a way that the button is held down) and still have instant access to momentary. Also I'd like to note that I have no problem using shortcuts, ramping, or constant output in momentary mode. I think people having trouble with this need to loosen the bezel just a quarter turn or less from the point where it goes into clicky mode. At this point you barely have to push the piston at all to get momentary and you can get the rest of the features by pressing all the way down.
Extreme:
The UI is my least favorite part of the Extreme which is a shame because I like everything else about it a lot. Baisically I want a light that I can have on my bed stand set to low for getting up at night to use the restroom or get water with out blinding myself. But, if I hear a bump in the night I want instant access to high while I grab my gun. My two problems with this light are as follows. First you need two hands to go from user defined to high, which is no good anytime you have anything else in the other hand. The other problem is, when I decided on the Extreme I was looking for something with quick access to high and I was thinking this would be like Fenix lights where you turn the bezel and get instant bright. I knew that if you turned the bezel when the light was on you'd have to wait, but I thought if you turned the bezel when the light is off you'd go straight to high. I didn't realize that if it was turned off in low and while it was off I turned it to high I'd still have to wait. This isn't a huge deal but it may be an issue to some. The other small gripe is that it's hard to get just the level of light you want when it's close to min because it takes two hands to turn the bezel meaning you need to be quick or clever to hit the button quick enough. Lastly, I know the fact there isn't a lock out is an issue to some. This is largely mitigated my a button that is hard to push far enough to lock on which is a plus IMO.
*edit* After using my Extreme some last night I must say that for certain uses and certain people it is a very good UI. It lets you have a high and whatever user mode you want and it won't unexpectedly change modes no matter how many times or how hard you push the button. It's perfect for all those who want a simple light. I just happen to like full feature lights with "smarter" UI's.
C2H:
This light has the least clever UI but I think it's implemented quite well. The ramping down feature means that I can keep the light in low and if I need high it's just two nearly instantaneous taps away. Also since holding the button for more then one second sets the mode in memory, you can use momentary without cycling through the modes as long as you hold for at least one second each time. This does take some getting used to however, because if you've been using a mode and want to go to the next one you have to let go, then press for less then one second to clear the memory then press again to get the next mode. Not hard at all once you get used to it, but a learning curve none the less. Pushing the button to lock required concerted effort on this light as well which I think is a good thing in any light which will be carried in a pocket.
Summary:
The C2H is going to be my carry light for a while. The combination of small size, tons of power, and a UI that can easily be manipulated one handed has won me over. As soon as I can get a clip for the EX10 it will become my light for anytime I want the smallest carry light possible. I still really like the extreme, it's smooth beam makes it the most pleasant to use indoors. It's my bed stand light and I'll just learn to set it to high before I turn it off since you can always go straight to low by loosening the bezel before you turn it on.
But I need to see it compared to an EagleTac P10C first 
