Earth. Earth is the most well rounded element imho. It isn't the BEST in too many aspects, but it excells in every aspect.
CC - Basilisk blood is fantastic
Shield - Diamond shield = 3 damage reduction
weapon - pulvy is pro as ever
rush ability - graboid, need I say more?
stalling - granite skin + protected diamond shield works pretty nicely
Permanent protection - only earth has this
Denial - quicksand, also puly a bit
Durability - most creatures are either burrowable or have tons of health
Earth only lacks direct damage CC and creatures with multi-use abilities, other than that its pretty sick.