The swing arm floats are fine as long as it's an older legitimate GM unit.
As much as the canister style sending units are sought after, they're very prone to problems with the float getting stuck in the canister. Especially if you are running today's garbage oxygenated fuel. This could be the reason GM only used this design for three years and then replaced them with the swing arm style.
I wouldn't worry about a bouncy needle on the gauge with the swing arm style either. This hasn't been much of a problem on any of the cars I've had them in.