Shouldn't this be in the polls section? Anyways, I have to say, I've used all three and all three had their own merits, so I have a hard time voting for the best. However, I will tell you Chandelure with Shadow Tag is absolutely broken and has no place in the game.
The haunted chandelier concept is PERFECT and I absolutely love it! Jellicent makes up a significant defensive core in the metagame and has the concept of royal jellyfish! I'm a huge fan of royalty and monarchy in general, and I love Water and Ghost types, so I'm a HUGE fan of Jellicent, be it male or female. As for Golurk... I have no idea how that thing is a Ghost. At all. But he's quite the powerhouse and his strange typing is quite cool. I've used him to some success and countered some prominent fighters with it, and his Focus Punch / Shadow Punch combo does a ton of damage.
In the end, I can't say who is the absolute best. If you think this way though, I've EVd a Jellicent to survive a Chandelure's Shadow Ball and OHKO back with a Scald or Shadow Ball with Stealth Rocks on the field. I used both Chandelure and Jellicent in-game. Chandelure was nearly impossible to train as it got shredded by nearly anything I was fighting (as Litwick it was too slow, as Lampent it was still fragile and Flame Burst wasn't cutting it), but Jellicent was "okay", just fragile on the physical side.