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Keypad, but when I looked they're quite a bit more than a key lock and with less choice.
You can get ones with a small handle which would be easier to open if you've got a bike in one hand.
Edit: you've just prompted me to look at the office-style keyless ones. Not actually that expensive anymore. Pending someone saying to the contrary I'd have a look at those instead. Keypads seem to be a bit of a pointless middle ground given that it's only a bit more for something much more convenient.
Double edit: Apparently it's a shit idea.
getting a gate built for my bike shed thing. I'll already have to unlock the bike itself - what is the easiest/least fussy lock i can fit on the gate whilst still remaining secure?