I'd go with the DBS V2. It's smaller in size, as mentioned above, the tail switch is easier to press, there are less moving parts, etc. The only reason to get the DBS V1 would be if you need the ability to switch between HIGH and LOW output with the twist so you could use the forward clicky to signal, etc, without worrying about modes changing. Or you could just get a 1-stage pill for the DBS V2 so you could signal without changing modes.
Now that the weather is finally getting nicer here I have been out for two 5 mile walks with the DBS V2 clipped in my front left pocket. I was wearing kahki cargo type shorts (lots of pockets, baggy, etc), so there was plenty of room in the pocket and it wasn't uncomfortable at all for me to carry around. YMMV.