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I have done both for lots of airlines, I find it depends on the check-in agent you get at the desk for quickness, Also the airline you are checking in and the service level of that airline.
Some airlines I have worked for have alot of extra baggage and the bartering takes up alot of time and also some airlines want you to have a quick chat with the pax.
Not blowing my own trumpet but I could do both about the same, I hated nothing more than checking in a flight and I had done 30 pax more than the other 1 or 2 agents, And dont get me started on seat plans.
I take it you are an agent then.