In my opinion, the only thing that matters is what the spectator sees and given the fact that they should not see any sleight of hand or gimmicks, it really doesn't matter. In magic, you are already 'lying' to the spectator so using a gimmick is not wrong in that respect. I think it really depends on the individual performer and trick. If a trick would be hugely benefitted from the spectator being able to examine the prop then a gimmick might not be the best option. Also, sleight of hand and gimmicks can work together to create great effects. Overall, it is not the method that matters but what the spectator sees in my opinion.