I hate the Sinnoh gym puzzles with a passion.
Oreburgh Gym: lol
Eterna Gym: In DP it was a huge pain. In Platinum it was easy as hell LOL
Veilstone Gym: Ugh... I despise this gym. It is so annoying. I always spend half an hour trying to figure out how the hell to get through it. Yup, I did it in both Diamond and Platinum. >__<
Pastoria Gym: Also a nightmare. If I hadn't read a walkthrough, i'd probably still be running around that gym trying to figure out what the hell I was supposed to do.
Hearthome Gym: Lolwut. Easy as hell.
Canalave Gym: The third easiest one in Platinum after Oreburgh, Eterna and Hearthome. Simple.
Snowpoint Gym: DANG SNOWBALLS! GRR I HATE THIS GYM AND ITS ABILITY TO WASTE MY TIME!
Sunyshore Gym: I promise you this. A few weeks ago I slept over at my friend's house, and it was about 00:30. We were supposed to go to sleep, but I kept on going through the gym until what, 02:00? Then the day after, I figured it out in five minutes.
Now.. for the other region's gyms (except Johto as I didn't play GSC and i've not come that far in HGSS)
Kanto: The easiest gyms ever. Pewter, Cerulean, Celadon, Saffron, Fuchsia, Cinnabar, Viridian.. the Vermilion gym is not hard, but annoying if you can't get it right
Hoenn: Also easy. The gyms in Rustboro, Dewford, Mauville, Petalburg, Fortree, Mossdeep and Sootopolis were all easy. I kinda have some trouble with the Lavaridge Gym sometimes, but I always get through it on my second try. Or third if I haven't played Emerald in a while. :P