I'm a fan of varied encounter difficulties, bouncing around between moderate and OMG you've got to be kidding me!, with the occasion difficult looking but easy to let the PCs feel like they are tough and getting better. (Even better if that can be against things they had problems with as a solo and now they can slaughter several).
This is both as a player and a DM. As a player a series of moderate challenge but no real risk encounters bores me to death. There's a real thrill and feeling of accomplishment (or at least feeling of relief) overcoming a really tough combat.
When I DM, I like to change up the parameters of battles so that different characters have chances to shine, and also characters may need to vary away from tried-and-true tactics to fit the situation at hand. Part of this is the monsters - hordes vs. solo, force composition, especially ranged or casters, another part is terrain, a third part is outside factors - time limits before reinforcements, people to save, a ritual to stop, etc.
I do like overwhelming but stupid forces (mindless undead, beasts) that the players can outsmart, just as I like really smart foes who use every advantage they can but are smarter then they are tough.
I often design encounters from hard to nigh-deadly (the English words, not the encounter building guideline keywords). But the flip side is that I roll everything in from of the players and I'm their #1 cheerleader and guy who says "YES" to their crazy plans. I hope the succeed, I just know that if they approach things in a predicable and boring manner the math is not in their favor.
In the 2+ years of my current campaign we haven't have a single death, though we have had plenty of knockouts and times when the players know that if they were a bit slower it could have been a TPK.
I try not to set up so that just a few bad dice rolls will kill, though I did almost have one of those recently. While fighting on an experimental dwarven zeppelin, the rogue failed several skill checks not to fall while doing risky maneuvers. After the last of them he would have fallen to his death except another character shot him with a harpoon from a ballista so he ended up dangling from the rope below the airship. He had enough HPs to take it, it was just a series of failed rolls that put him in that place.