Far and away I recommend the Crimson Trace.
Nothing else to manipulate, just grip the pistol and it's activated. Most of the accessory rail based lasers require activating and deactivation with another hand or motion and risk you putting your hand in front of the muzzle or finger right about the trigger.
The rail mounted options also become an all on or all off proposition. The Crimson Trace is activated and deactivated by applying and releasing pressure on the grip.
Most importantly, the Crimson Trace system will fit in most all standard holsters, the rail mounted ones do not.
Have I convinced you?
Jimmy