Don't know much about Brennan, but I've read a LOT about Vatanen lately. He's a big favorite at HFboards -- lots of folks there are excited about his offensive potential.
A word of warning though -- he's a little gaffer. I think he's put on some pounds, but he's generously listed at 5'10"
Points-only, Full Keeper Dynasty League
Active roster (no starts, just total points): 12 FW, 6 D, 1 Goalie
Forwards: Ovechkin, D. Sedin, Stastny, Nash, Kesler, Ribeiro, B. Richards, Selanne, Hossa, Fleischmann, Whitney, Lecavalier, Alfredsson, Okposo, Plekanec, Doan, S. Kostitsyn
Defense: Goligoski, Campbell, Gonchar, Bergeron, Liles, McBain, Vatanen, Timonen, Visnovsky, Giordano, Wideman
Goal: Luongo, Holtby