Left arm. If I don’t get to chose which side, then leg.
I’m pretty sure I could learn to type on a one-handed Dvorak keyboard much better than I could learn to dance on a prosthesis.
I love playing bass so I would definitely choose to lose the leg.
Me too. Not only do I love it, but have even been paid for it once or twice.
I love to run and play sports too, so this makes the question rather difficult.
I will have to go with leg on the info. presented by Brynda.
Leg.
A few years ago I tried to take an air conditioner out of a window by myself. My hands slipped and both arms went through the glass, resulting in 50 stitches in my left wrist and 19 in my right arm. Knew I was cut right off, but not how badly, so I ran in the bathroom and stuck my arms under running water.
Nasty.
The last thing I remember is looking at the tendons in my left wrist and thinking 'Wow, that’s really neat!" Fortunately a friend was there or I would have died from blood loss.
After being stitched up, sitting at home in my recliner - it was awful. For the first few days - till the swelling went down in my right arm - I was helpless. Couldn’t bathe myself, couldn’t brush my teeth, couldn’t wipe my…you get the picture. I am very lucky - Mr. SCL is a RN so at least he was used to physically caring for helpless people.
Definitely leg. The worst part about breaking a bone in my foot was having to hang the leg out of the tub while I took a bath. And sitting front row at a hockey game the night I forgot to put the big stretched-out sock over my poor little piggy toes. They were blue by the end of the game!
Leg, for the reasons already mentioned plus it would make my john-thomas look bigger. 
I must go against the consensus and say Arm - preferably Left Arm. The dang thing isn’t good for much anyway, I can’t even open a pop bottle with my left hand. If I had a choice I would say just lop it off.
Well, as someone who lost a leg above the knee 18 years ago, I will definitely say leg.
I am still able to work in my profession without much of a problem. (Just don’t throw my leg on the roof and hide the ladder 
I couldn’t imagine losing an arm (shudder)
Leg, no question about it.
You need two hands to play most video games, especially FPS games. You can’t drive a stick shift one-armed. And if I lost my right arm, it’d be like losing a wife of 13 years.