The 50mm for 2 reasons. More light gathering power means easier to find those faint objects, and if you have some light pollution, then a 50mm is really a must, with light pollution a 30mm is to small.

I have a 9X50mm and never looked back. One my old scope it had a 6X30mm and quickly changed it to 9X50, a hugh improvment and found it a lot easier to find to use.

A 30mm finder I feel is to small, get the 50mm.