I use a double trolley. Invalid Link Removed
Really expensive, but I sit when I play, so it's great to have a buggy + a stool in the same thing. It's very sturdy, too. I take busses to and from other cities a lot, and in the bottom part I can lay the bass on its back without it being damaged because of the large wheels. It can be heavy (and cumbersome), but I take Montreal metros (where we don't have elevators except for 4 stations), go up and down stairs, escalators, etc, and I can handle it. I don't have a small bass either.. I have a big and heavy 7/8 orchestral bass. I'm young, so I guess that makes a difference, plus I cycle a lot so I'm fairly strong.