Oh neat, a Q&A prompt. Let's see...
I'll rank maps by difficulty from 1 to 10. 1 being the easiest, 10 the hardest.
M1 - 8/10 - This one is pretty high up there because of no berserk or saw and limited just about every resource coupled with some very nasty encounters.
M2 - 6/10 - Berserk is way too deep into map, requiring to run through a bunch of nasty claustrophobic spots before reaching it.
M3 - 4/10 - Quick berserk and straighforward, cyber battle is rather trivial.
M4 - 9/10 - This one was a fuckfest. That spider is in a spectacularly miserable position along with a huge chunk of map, ammo had to be harvested to beat it comfortably and the final ooze section with radsuits makes this a major pain in the ass. I've barely made it in the successful attempt, even mistakenly wasted one radsuit because of chainers.
M5 - 3/10 - Rather easy after figuring out I can wake up some deaf monsters in that hallway with blocking mancubus. I've tried to reach somewhat decent time here.
M6 - 5/10 - The last cyber can be very nasty even with those invulns, otherwise unremarkable. Given that he is right at the exit, this can be a pain.
M7 - 6/10 - Despite quick berserk, there are some very nasty fights towards the end.
M8 - 4/10 - The scenario around berserk can be difficult and AV in the open is a sucky spot. Other than that, rather easy.
M9 - 7/10 - Berserk is again almost at the exit, so it takes quite a lot of effort to reach it. And the clean up afterwards is also tough and health is limited.
M10 - 9/10 - A miserable chainsaw experience, lack of health, tons of cacos and hitscan in very ugly encounters, with the worst being right at the exit.
M11 - 8/10 - Figuring out those cybers was a huge part of difficulty, that revenant's placement is the only reason map even turned out doable. Berserk is deep into map and there are still quite a few tough spots even when ignoring the cyber trio.
M12 - 7/10 - Not that bad, berserk is rather close-by and individual fights aren't that cutthroat when taken slowly. Cyber's arena offers quite enough space. The map is still massive and the final room can go very ugly.
M13 - 1/10 - Not worth a comment.
M14 - 2/10 - Very easy, got a good time here because of great infights at the very end.
M15 - 5/10 - Berserk is at the start, no seriously hard parts, occasional claustrophobic sections. Arena with two individual cybers at the exit offers a lot of space to beat it without too much headache.
M16 - 3/10 - Easy, the only hard monster is that one baron. If he follows you out of his tiny room, it's almost impossible to take him out other than pistoling.
M17 - 6/10 - Reaching berserk requires getting through some claustrophobic heck and cyber is in a very delicate situation, because it's almost impossible to punch out due to those teleporters and there's barely 200 bullets, so this was quite a puzzler. Not so hard once I had it figured out.
M18 - 8/10 - Berserk is again almost at the exit and reaching it fast is impossible due to ridiculous claustrophobia and some terrible fights. The hardest section is accessible only once via w1 teleporter and houses a PE, caco, rev and manc that have to be taken out with basic fist and limited ammo. Overall this was a cutthroat sudden-death fucker.
M19 - 9/10 - Despite quick berserk, this was a very heavy endurance challenge that looked rather bleak in terms of doability. Besides cyberdemon, no section is hard on its own, but as a summarization it's very high up there. Cyberdemon itself was a headache and my way of handling him was unreliable for how far into map it's encountered. If I were to pistol him, all the unreachable monsters would then pose a serious problem and much more infighting would be necessary to instigate.
M20 - 7/10 - The overcomplicated progression and finding a way around it was the main difficulty here rather than raw battles. It's still quite a drag and last fight with caco horde in enclosed space can go bad.
M21 - 3/10 - This can be very easy if you take things slowly. Joe got 19 here so I've decided to push for good time. In the end, getting 9 turned out rather hard, because of some headless risks with some monsters that I really didn't want to pistol out.
M22 - 10/10 - This was the worst of the worst. An endless endurance challenge with 4 cybers that I've realised can be taken out by pairs rather than all 4 altogether. All of them are beaten basically by raw punch-outs, I couldn't figure out any way around this. Getting berserk placed in very last room was also a feat in itself, because it required awkwardly avjumping to bypass vast majority of map to reach smoothly.
M23 - 8/10 - Some closed off sections here, like caco heaven with 33 cacos and 4 mancs in that miniature room are the main sources of difficulty, but it's nowhere near trivial even when disregarding those. There's also a bunch of free-roaming viles, claustrophobic bits, berserk far into map and mastermind that doesn't die on its own very often.
M24 - 9/10 - The ultimate challenge in tedium. There's a metric fuckton of unreachable heavy monsters and 2 cybers. Nothing about map is hard on its own, but is a terrible ordeal when judged in its entirety.
M25 - 7/10 - Ignoring the obtuse progression, most of difficulty here stems from enclosedness of almost entire map. Fights in tights spaces can go wrong in an instant and waste an attempt before you know it. Forunately, it's not that lenghty.
M26 - 8/10 - Some heavy open fights at the start and some gimmicky fights in enclosed spaces later then finished by an irritating open section with drastic height differences makes for an overall unpleasant recording here. Quite difficult.
M27 - 7/10 - I was seriously demotivated when I've seen the absolutely retarded progression I have to learn here. Once you bring yourself to it, it's not that hard to pull off, with only few sections sticking out as difficult.
M28 - 8/10 - Again, tight spaces are the main difficulty here. Berserk is in an especially difficult to survive spot. I figured out one cyber can be stuck easily fortunately, otherwise this would be close to impossible to beat.
M29 - 6/10 - This was surprisingly simple once I've figured out progression, with very few rough spots, lack of boss monsters and overload of bullets. That teleporter which randomly teleports non-flying monsters into an unreachable pit is facepalmworthy.
M30 - 9/10 - A very different nature of a map compared to all previous ones. All sections could potentially cause trouble, because you have to handle every single monster by yourself, either by deliberately making infight or personally handling. Couple that with an overly complicated progression, then 3 cybers, one of which is in an especially terrible spot, then to top it off, an IoS that has a very tight window for autoaim to register and you have a recipe for disaster. It still doesn't top 22 in terms of difficulty and time spent figuring out and trying to scratch off to-do list.
M31 - 7/10 - There are some ugly scenarios, very tough start and some monsters teleport completely randomly to certain destinations, but there's still an overload of powerups to make up for it.
M32 - 3/10 - Not that hard on its own, but I couldn't slowly pistol out some monsters, so I've handled it in a way that was rather irritating and hard to survive.
That's about it, even in that order.
Tough question, I think no map has really grown onto me that much to stick out as a favorite. I'm a fan of clean simplicity, and going by that, map 1 would be the most fitting into that description. As for demo, I guess 30, but that'd be just because it was the last gap to fill.
Nothing in particular motivated me really, heh. I just start with something and see how far do I manage to keep up before abandoning stuff midway through. I did map 1 just because not even a single map had a tyson of it done. Then I've had the idea to check maps in db and figured out 30 out of 32 maps actually contain berserk.
That's about it, sorry for boring answers.