Nothing wrong with any of them. I like Skarner because he's strong at all points of the game and can build between support and tanky dps. His aoe perma-slow is just nasty and he is great for diving the enemy carry or kiting for his AD.
"Happiness is nature's way of telling human resources you're overpaid." - Catbert
To master Skarner and Hecarim you must master the skill of pushing the Q button on your keyboard for hours.
Hecarim is weak as hell early on but can carry harder once he gets a couple core items like spirit of the lizard and frozen gauntlets.
Skarner doesn't really need to build heavily into damage and just outlasts others through his constant Qs and autoattacks with his shield being up often from his passive. His slow just stomps anyone that gets caught in it and lets his team follow up.
The problem with Skarner is that the bastards at Riot (I'm looking at you Morello) nerfed him during S2 when he was still good where tanky junglers like Amumu and Maokai were stronger and left him for dead at S3 where bruisers are the better choices, oh and he has to be in melee range to do anything so he has more trouble getting close but at least he is tankier.
tl:dr if you are new at jungling then Vi isn't a bad choice but if you are willing to put work into kicking ass then you may want to consider Hecarim. Skarner is only reserved for heroes like myself so stay away from him.