Looking at the disconnects for central AC available from Lowes online I notice that most are listed as 60 amp. That seems a bit overdone to me. Does a typical 3 ton unit for a home need anything more than a 30 amp disconnect?

I needed to free up room in the sub-panel to add a new circuit, so after noting that the dishwasher and garbage disposal were on separate dedicated 20 amp circuits, I decided to combine them on one circuit, after checking the amp requirement for each and determining that they would not overload a single circuit. My question is what is the best way to combine two circuits in such a case? The fuse for each was in the same subpanel, so I moved one of the black wires to place it under the same screw with the other black, thereby combining the circuits. I could have also wire-nutted the the two blacks together (staying inside the subpanel box), then pigtailed them to the screw. Is either method acceptable and is one better than the other? Thanks.