I like the idea of a keeper league since this is an annual thing and most people that play this are the same every season... and it also motivates anyone who is doing poorly in the season to keep active and make moves for next season.
If we do go with keeper, we have to decide on what rules we'll use (like: how many players can a team keep? will I sacrifice a draft pick by keeping a player? ... ...). I don't think has to be decided now, but should be decided as soon as possible.
I have never played keeper before, but it certainly looks interesting. If it doesn't work we can always just go back to the same format!
So yeah, I vote for keeper league :P
Basically: Do this season like we have always done it, but we get to choose keeper players for next season from the players we have this season.