Pay tax where users reside
Where users reside is where the infrastructure is used, where they have been educated and because useful fodder for the surveillance industry (aka Google Facebook, LinkedIn and all the other US outfits that say "it wasn't me" as soon as you start talking about privacy), so pay tax there.
The problem is that tax and being taxed has always been a dodgy subject as those who have much would like to keep more than Burt cleaning the streets. I'm no economist (which will probably be clear in the next bit), but I'm wondering what would happen if tax percentages stop increasing from a certain level - the prime reason I see very well off people and companies dodge tax like a devil dodges holy water is because it just keeps going up.
Getting 25% of something large versus the barely 1% that's left after all the dodges strikes me as more productive, and less work supervising.
Yeah, yeah, it's too simple, plus it would kick a lot of accountants out of a job. But I still think it's all made too complicated.