Personally I will go for the thumb safety. I don't consider that lever in the middle of the trigger much if any of a safety. If I don't train my mind using the thumb safety while practicing then I shouldn't have the gun. I would much better train using a thumb safety then expect that trigger lever to keep me from possibly shooting myself.
To each his/her own what they feel is safer for themselves. It's their leg not yours. Personally I carry a revolver because I feel it is the safest and most reliable gun.

An external thumb safety or any safety for that matter will not stop a HUA moment of action.