Back in the day...
In the beginning of BtVS Angel's hair was a lot longer and very gelled.
Angel's hair got a bit wilder and less gelled.
In season 3 of BtVS Angel's hair was less gelled and a bit shorter with bits out to the side.
In season 2 of Angel his hair was more gelled.
In early season 3 his hair was a bit less gelled and shorter at the sides.
Towards the end of season 3 Angel's hair was only gelled at the front and longer all over, especially the sides.