I'm not sure this directly answers your question. But your solution is going to depend entirely on what you do and how you do it.  Dad had wrenches in a roll (my wife made him one of heavy material for a Christmas present after his plastic roll fell apart) 2 socket boxes, a couple screwdrivers, a hammer and a couple adjustable wrenches.  But Dad was a shop mechanic.  If you couldn't fix it with those tools you took it to the shop.  Not everyone has that luxury. 

I've tried about everything you can think of. Besides working on the farm I've worked on copiers and been a propane service man. Those taught me part of the answer lies in where you are working and how you use your tools. If you are able to drive up to where you are working and work right there the best solution is different than working in a customer's home or office.

My preference from years of experience is a pickup truck with a service bed.  But that is not always the solution for everyone.

My first pickup was a 68 Ford (it wasn't so old back then) with a camper shell.  Insulated with a swinging door.  I bought a Sears Craftsman toolbox and mounted it inside the door.  Compared to what I was used to I was fully equipped.  Next truck had an across the bed toolbox.  At one time my pickup was a 1 ton Dodge Maxi-van.  It had a bench seat for the kids and the other 8-10 feet was cargo space. I was selling seed corn (pre-forklift days) and you could put 60 bags of corn inside, take 3 kids along and go deliver corn. working on the farm you could put all your tools inside and lock the door.  They were out of the weather and secure.   I also worked out of a Ford Festiva (in my copier days). WAY different set up. But it also was a very different set of tools.

Over the years I've has across the bed toolboxes (BTW these are just photos I've found online, not mine) 

side mount tool boxes

 deck boxes (probably not the accepted name)

My current pickup has 2 Montezuma boxes because 1 will not hold enough inch and metric tools (they are different models than the photo)

My kids went together and bought me one as a gift.  After using it I bought the other one from a friend's brother in law.  The down side is it limits your cargo capacity and to be usable either need mounted on the side of the bed or be in the back.

As I said, I've tried about everything you can think of.  Part of the answer lies in how you use your tools. If you are able to drive up to where you are working and work right there the best solution is get a service bed on your truck. I've had 5 over the years, everything from a 6 foot bed on a Ford Ranger to a 10 foot bed on a 6x6 dually to this one I bought at a sale earlier this year.

I wasn't looking for a truck.  Kind of glanced at it.  They started bidding and I just couldn't pass it up.  I didn't steal it ...  got close though.  I bought it worth the money.  It was set up pretty much like my dream truck. The big downside is it isn't a very good daily driver.  It's more of a mobile shop on a Chevy C-60 chassis, with welder, air compressor, fuel and oil storage, crane, etc. It proved its worth this Spring when the choice was hit oncoming traffic with the Tilloll or bounce the transport wheels in the ditch.  Broke the right side transport cylinder mount off the frame.  I'd call it a bad weld but it's lasted 15+ years.  We got it off the road, looked it over and called a retired friend who is a lot better welder than I am.  Asked him if he could meet us there and this truck would be there.  He was like a kid in a candy store.  A little grinding and welding and we were going again.

Getting back on topic, if you are not working right there, you will still be carrying a tools to the work site. The best water resistant tool box I've found lately is a DeWalt One Touch.  There are heavier models but for my use this one os the best value.  I use it as a project box.  I can throw the parts and tools  in it for a job and haul it in the bed of the side by side. The gasket lid keeps everything dry and clean.  Right now I have one full of electrical stuff to install an new outlet on a landowner's grain bin.

But I am a big fan of Milwaukee's Pack Out boxes.  I have 3-4 four on the new service truck (again not mine, a stock photo)

I use the smaller ones as go kits.  They stack together for storage but I can grab one and run.  I better explain a go kit.

I like to make go kits.  Most of them are for battery power tools. The idea is you grab a kit and everything you normally need to use it is there.  My 3/8" battery impact kit has a set of inch and metric sockets plus 7/16, 1/2, & 9/16 wrenches and spare battery in it.   My 1/2" impact kit is has inch and metric sockets.  A drill kit, it has drill bits and screwdriver bits.

When I was servicing propane I had a pilot kit in a little plastic tackle box with the usual tools and parts to work on a pilot light.  Our propane trucks had a meter with a printer that often needed a little attention when you were 40 miles from the shop.  I had a little pocket size box in the cab with the odd sized wrench and Allen wrench needed to work on it plus a couple spare machine screws to replace the cover screw you inevitably lost.  In my LP service truck I had a kit for tank gauge repair that included bolts and gaskets, the jig for drilling out broken bolts, the correct drill bit, etc.  On and on.

It costs a little to do that and takes a bit of planning and room to store it, but it greatly increases efficiency.  You are not spending 10 minutes searching and gathering parts for something you do regularly.  And when working in front of a customer you look much more professional than going "I know I have one of those somewhere."

If you are going to use a pickup or flatbed I recommend the Montezuma.  You'll want to hang the tools instead of keeping the roll. And you still need a place for the go kits and supplies.  And it still doesn't do what a service bed will do.  Like I said, once you get a service bed you'll never go back to a plain pickup without going "Boy I sure do miss my ..."