Now there are a few rules here.
1: You must have entered the pararrel dimension at least once.
2: No hell.
3: No going like "Z0mg d4t P[) 1Z 5o 34Zi I g0t thru 8l1ndfold3[)!!1!"
4: Please refrain from posting PD'S 6, 16 and 92.
Now I shall start:
PD.0: Currently the hardest non-hell PD I have went in, as I have yet to beat it. 9.5/10
PD.3: The second easiest PD for me, only the fallen bobbles sometimes give be a little trouble. 2/10
PD.11: A tad annoying, but otherwise relatively easy for me. 3.5/10.
PD.13: Don't remember going in there recently, but not too bad. 4/10.
PD.15: A pretty tough PD, not as tough as the PD you need to go through to get the key for it, but still up there. 7/10.
PD.23: Easily the third hardest PD I have gone through, the razors and the skill needed to get through is nasty. 8.5/10
PD.25: Nothing to say here except it's annoying when you lose because of a stray bomb you can;t do anything about. 5/10.
PD.26: A relatively easy PD, some nasty parts but otherwise easy. 3/10.
PD.42: Ugh, tough one. That's all I'm saying. 6.5/10.
PD.43: At first a tough one, but it gets really easy really fast, with only one level (43.6) being really rough. 4.5/10.
PD.46: Lots of razors and many times where it's hard to evade dying. 7.5/10.
PD.51: I have lost my skill with this PD. It's not AS bad as it would be normally, but it still is a toughie. 7/10.
PD.55: For me, the easiest PD of all. Even with

PD.63: I have not gone in this PD in a REALLY long time, so I will not rate it.
PD.64: A medium difficulty PD, the easiest of the 3 PD's (PD 46 and 15). 5.5/10.
PD.72: The PD in the PD is really easy, but some of the levels in the first PD are not as easy. Still, an easy PD. 3.5/10.
PD.74: Same as PD.63.
PD.77: Second hardest PD, and I'm saying that because I have not gone through the first level of it yet. 8.5/10.
PD.97: A bit tough to evade the razors, but a pretty easy PD otherwise. 2.5/10.