Quirion Dryad and it isn't even close. Grows really fast in a low-cc environ. Kudzu is a bit too lazy and one-dimensional; play lands, or maybe a Harrow, I guess? It's mostly quite a slow grower, though. Dryad doesn't have that issue; she can shoot up several +1/+1 counters each turn, depending on deck composition. She's also really "fun" in that regard, which is valuable.