I used to have an open shelf tool cart but I found that during a job, I would fill it quickly. Organizing all bolts/nuts that I removed and laying in components that are removed. For that, anything that has 2 shelves and 4 casters would work, depending on size and ability to handle weight, like
@mountie said. I ended up getting a larger 5 drawer US General roll around tool cabinet with the top that is exposed when lid is unlocked and raised. The wrenches and sockets/ratchets, that I use the most, are in that cabinet and I can roll it up to my work easily. It also has a bottom shelf that I store fluids and lubricants that I use during jobs, too.