I agree with 2nd Gear.
Drawer layout is what you want to consider most of all.
Cubic inches is a measure of the overall dimensions of the toolbox (more or less). It would basically be the same number if it had just one gigantic drawer. That isn't particularly helpful.
Weight capacity can be helpful, but it depends which number you see. Some list overall box capacity (less helpful), and some list capacity per drawer (much more helpful). Generally you'll see 100# per drawer for this level of box, give or take. Better boxes hold more, lesser boxes hold less. You may think that's an incredible amount of weight, but start adding sockets together and you may be surprised by how much it adds up to. Even if you're not at the limit, better drawer slides will likely be able to hold the weight day after day for longer without failing.
But back to drawers. The ideal layout depends on you, the user. Do you have a lot of sockets and do you want those to be in the top drawer of the bottom box (most accessible)? Then you probably want that to be a drawer deep enough (height-wise) to hold your sockets upright on holders. Do you like your tools to all be laid out flat like an aircraft technician (slimmer drawers)? Do you plan to store bulky power tools in the same box (one or two deep drawers)? Perhaps a side cabinet, if applicable, can handle this stuff? Do you want a pegboard (again, depending on which box)?
These are all questions to ask yourself. Then again, it may seem like a big decision, but it's not the end of the world. If you buy something and end up wanting something else instead, there will always be ways for you to make that happen.
In my experience, the milwaukee boxes are more expensive than the husky boxes, but I think the name plays into that a lot. In general I think they are close in quality, enough where a sale price makes one more attractive than another.
