He's different from Yaya though, he's more of a good balance between attack/defence, while Yaya is probably better defensively than he is attacking, so you can't completely compare them, it's not fair to. Yaya is exactly what Barca need, Essien wouldn't fit in, as good as he is. Chelsea is the perfect club for Essien at this point in time, he's exactly the type of player that we need in our midfield. Ever since Essien came back from injury we only lost 1 game, that says more than enough.
To sum it up, Essien and Yaya are different types of players but equally valuable to their sides, though I'd rather have Essien 10 times out of 10 over Yaya unless Yaya was the EXACT type of player needed for my squad.