OK I'll bite - first things first is that, by and large, I have been mostly a collector, user, buyer and seller of EDC lights which, for me at least, means a pocketable light. Consequently, I tend to favor the less than 4" lights so a light has to bring something to the table for me to deal with a larger light - those things conventionally being either more power or longer runtime (not sure there is any good reason for a larger light although some like the feel of a 2 cell light).
Predominantly for me that has meant a 2xCR123, 17670/18650 light. I have a few Minimags floating around with various upgrades but they are backup duty only really.
I can narrow it down to the 6P (and relative clones) form factor and the E series form factor (E2 derivatives). They bring different things to the party - the 6P (P60 drop in) lights are really versatile. Numerous drop in options, numerous battery configuration options, numerous add ons and extensions and upgrade paths/options. Plus you can in a still small package drop in a really hot emitter due to the relative mass of the light and build a flamethrower. However, they are a bit chunky overall.
The e - series lights are a different beast - lots of lego possibilities (including dropping down to a 1 cell format that is truly pocketable, I don't consider the 6P bezel on any one cell body to be much of a pocket light) with the E1 bodies. However, upgrades generally mean an entire head or a mod job, neither as inexpensive as a P60 compatible drop in. And you are more or less limited to a 17670 as your largest rechargeable (in a SF body at least, aftermarket 18650 bodies are like hens teeth and even SF bodies aren't exactly a dime a dozen, but there is the aleph option). But... and this is a big but... the form factor. The E2 bodies are really compact, but still comfortable in my hands, and the e heads are a thing of beauty. The combination is a slim, still easy to pocket, nearly perfect light. I think that the e-series is more fun too and more practical with lots of single cell possibilities.
My vote is for the Surefire E-series and compatible 2 cell lights - my personal favorite at the moment is a Z57 with an E2E body, a KX2 Milky Creemator head and an AW17670. Lots of oomph when you want it, plenty of runtime at low levels and realistic runtime at higher levels compared to the relatively short runtime on a single RCR123.