Felicity - S4 definitely. Her hair looked great straightened out.
Ben - The buzz cut he sported after returning from EMT training in S4. That looked sooo good on him.
Sean - His hair always looked fine to me.
Elena - The braids looked amazing. The styles she did with them were fantastic.
Julie - Hair hair didn't change much. I never really took much interest or cared for that matter.
Noel - The short cut he had during S2. He looked really great.
Meghan - I hated the crimping. I hate crimped hair. Meghan's hair looked great in S4.
Greg - That whole fluffy thing he had going on was horrendous. He looked so much better after he cut his hair.