The IMR or "Improved Military Rifle" powders are seeming pretty old school these days, but they have a lot going for them...
They are extremely consistent, lot to lot. Ask any of the techs at Sierra, and they'll likely tell you that the IMR powders are the most consistent from one lot to the next. That means a lot--pun intended.
Paul Box at Sierra once told me that the IMR 4895 was the most consistent powder they had ever used, from one lot to the next, it stays the same.
I realize that the IMR powders are not "Extreme" rated, but with that "extreme" rating comes some other unwanted issues, such as lot inconsistency and ignition issues which cause these powders to like a case full so they'll have plenty up against the flash hole. Varget is a great powder, for instance, when you stuff the case to 90+ percent... but in lesser volumes, you can get some pretty crappy ES numbers.
Reloder powders are pretty good, but folks at times report lot variations with those.
VV powders are really great... but not as commonly available as other options, and the 2 pound thing is a minus when considering one of those powders for load testing. (They only have it in 2 pounds lots around here, anyway)...
So if I have the option of using an IMR powder formula, that's what I tend to go with. It's consistent, it's easy to light... and sure, it's a bit temp sensitive but you need to learn trajectories for cold weather anyway--regardless of what powder you're using.
So I vote for IMR. Give me 4895, 4064, and 4350 and I can pretty much do what I need to do.