Hand wash of course is the best since one only uses recommended car wash materials as recommended by BMW.
As for the touch free or other car washes one never knows what effect the cleaning detergents they use has on your many retractable hardtop seals. Keep in mind that seal deterioration will only happen as time moves on.
When I had my Z4 and did not have time to hand wash I used a self service car wash that has the high pressure nozzles and only used the "Rinse" to clean the car dirt off never the soap option.
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