Yeah, I was really excited by Golurk's typing and how cool it looked before I knew anything about it. Then I saw its speed stat.
One word: tank. In fact, I made sure to get a Brave Natured Golett when I hit the Dragonspiral Tower. I knew Riser wouldn't be speedy so I decided to take the hit there.
Liepard, no contest. I was actually excited for an early Dark-type Pokémon, I didn't think it would be an awesomely strong Pokémon, but at least usable like Mightyena... Of course, I was terrible wrong.
Cofagrigus and Golurk too, I am not sure why, but I couldn't proper use them? Jellicent worked way better for me, so did Chandelure.
Oh heavens, Liepard. >.< There are no words to express the disappointment that is Liepard. Purrloin's adorable but can't stay alive. It's even worse after evolving.
I can't speak for Cofagrigus, as I've never really used a Defensive-type Ghost but Golurk worked wonders for me. I pitched a lot into Riser's Attack and filled the rest in with Defense and Sp. Defense EVs and it worked; he took down Ghetsis for me. Seriously, the big guy was a killer. If it moved and I said, "Destroy it", Riser beat it into paste. This is not an exaggeration, either.
Pansear. :/
If you fail to OHHKO a Pokemon that's 4x weak to your STAB Move, and it OHKO's you with a move you resist, there's a problem... :/ (Incinerate sucks)
Ugh. Don't go there.
I got my Pansear up to level 38, thinking things would eventually get better and they didn't. I finally Stoned thing, got a Simisear for the 'Dex and shoved it into the deepest, darkest recesses of my PC. It can stay there and rot.
Haxorus was a disappointment to me, honestly. I grabbed one via GTS that happened to be level 100, fully EV trained and perfect in Speed and Attack.
It kept getting killed by Scald and Overheat. Yeah, didn't keep that thing around after that. I ended up trading it for a shiny Golett and I have no regrets. Same story with my Hydreigon: it kept getting its butt handed to it while I was training it so I traded it off to nail a nice shiny Golurk that was on GTS. Again, no regrets on my end.