First of all, you will not go wrong with eighter car.
I think the E46 M3 is an ageless car in every single aspect. So will be the E92 M3. The E92 M3 imo, has compeleted the downsides of the E46 M3. Just like the E46 M3 perfected the E36 M3. But unless you drive the E92 M3, I really doubt you will think this way and make a proper decision. Because for many, E46 M3 was, is and will be one of the greatest cars of all times if not the greatest. So it will be hard to leave the E46 and move to E92. But you won't regret it once your get a feel of it.
Good luck and don't forget that you won't go wrong with eighter choice.