Is Raspberry Pi 5 16 GB the best one can get right now for tinkering?

Best if you need the RAM and are willing to pay, but it doesn't make as much sense as a mini PC for the same purpose (cost-wise), if you're doing normal computing tasks.

I think the sweet spot for the Pi 5 is 4GB (cost vs functionality you can use it for). But if you're like me, you don't care about value quite as much as fun/exploration. And for that, the more RAM, the merrier...