is it me or what but i think that there should be two different hoppers in btb. one for slayer and one for objective. im not the one who quits out when slayer is picked but it seems like all that people pick in btb.
All I seem to ever get are Objective games in Reach BTB. No Armor Lock in Objective and that makes me sad. 
I don’t think the solution for this is having two different playlists. It helps a lot going in with a party. That way, you can get what you want about 70% of the time.
I do understand your frustration, though.
best idea, go in with a party. i only go in with a group of my friends. we pretty much always play what we get. its usually objective though. but its more fun for me as we get to play a little longer. instead of just 100 kills, we usually end up getting almost a couple hundred and the game is much longer as a result. =)
go in with a party.