I'd argue levels that are difficult due to layout are the best. They almost act like a puzzle game, as the game challenges you to work out how to finish it, and when you do, it becomes relatively simple, and then speedrunable.
7-19X: XOXO is a perfect example of this. It's always listed as one of the hardest levels in the game, but one you get the trick to the upper level jumps, it's quite easy.
I'd argue the Kid levels fall under this blanket too, of course I've only ever played the first one.
Once you figure out each of the jumps, it's muscle memory. Of course, it's very precisely timed muscle memory, and it's still very easy to fuck up, but it still fits the model.
Uh...the kid levels definitely DON'T fall under that blanket. It's constantly "I know where I want to go, I just need to...GAAAAAAAAHHH".
I do prefer the "puzzle" type feel. I love a good challenge, but I get pissed when the hardest part of the level is at the end. If the level is the right kind of challenging, by the time you get to the end, the only thing really working against you should be yourself, the pressure and stress of the situation. That's challenging enough sometimes...
"Yes, I finally made it!!! Okay, just one final jump over this buzzsaw...a little...not too...GOD DAMN IT."
If it's the wrong kind of challenging, you speed through the level, no problem, and then get to the bottleneck at the end. The amount of time it takes to get there + the repeated failures make you sloppy, and then you're dying in the beginning of the levels for no reason. That's why 7-20 took me many, many times longer than 7-20x.