Vehicle importing, when coupled with either delivering collections or using the even more profitable top-range only method (which we will discuss below), will grant you great payouts while also leaving you time to do other activities, such as the two most efficient CEO missions, Headhunter and Sightseer.
The wonderful thing about coupling these methods is thanks to the way their cooldowns are set up. When you complete any CEO mission, a global timer is set on all CEO missions, with another, separate, longer one set on the one you've completed. When you play a round of Sightseer, all CEO missions go on cooldown. Complete an Import/Export mission, whichever is needed be it an import or an export, and when done with that, Sightseer will still be on cooldown, but Headhunter won't.
So, you go complete Headhunter, and then an Import/Export job, then Sightseer, then another I/E job, then Headhunter and repeat this cycle for as long as you want. Using this method, players have reported incomes of $GTA 420,000 and 430,000 per hour on several threads, with detailed run-downs of timers and profits.
This is something that's wholly achievable, but you'll need to learn the ropes. You'll need to memorize ideal techniques, spawn locations, routes and more to run both the Import/Export missions and the CEO work in the best possible times with the least possible loss in terms of repair costs on the former, but once you get the hang of these methods, the money will be pouring right in.
So what about that Top-Range Only method we mentioned before regarding importing and exporting vehicle cargo? Basically, it's a technique used to maximize profit when exporting vehicles by ensuring that you only roll these top-range rides when sourcing new rides.
Basically, this just uses the game's programming to full effect, so there's no glitch or exploit here. Basically, Import/Export draws from a library of 32 cars. So long as you don't have all 32, when you source a new car it will always be one you don't have yet. The idea is that you fill up your warehouse with precisely one of each ride, resulting in a full set of 32. Then, all you need to do is sell those which bring in the most cash, one at a time, and the next time you source a ride, you're guaranteed to get the same one again. This way, you don't need to resort to lobby-hopping to roll the best cars each time.
This is currently the single best and most efficient way to make cash in GTA Online — it is the ne plus ultra of earning in the game. One alternative is exchanging the CEO missions with managing a business from the Bikers update, however sometimes you'll need to spend more time with that than a cooldown, kicking up the routine. Sometimes you'll grab bigger profits than with the method outlined above, but at other times you'll lag behind, and overall, at the end of the line mixing CEO missions is the better alternative.
So there you have it folks, the final result. Import/Export missions and crates on their own are roughly identical when done well, but the former allows for greater expandability through the addition of CEO jobs to boost your money per hour ratio, making it the better choice overall. Not only is Import/Export a return-to-form for GTA Online, once again placing the focus on the stealing of cars, but it's the best way to make cash in the game too.
So, whether you want more cash to your name or more downtime in between cooldowns to do stuff you enjoy rather than what pays best, Import/Export is the way to go. After all, we're all playing to have fun, so if you're not particularly hurting for more $GTA, you can spend the additional downtime with whatever in-game activity it is that you get the most fun out of. Happy exporting!