"Consistently" is hard, people's experiences tend to differ with every company out there, even by what country you're currently in. For example, I've always had quick and reasonable replies from Coinbase support, but I know friends who've had the complete opposite experience with Coinbase, so won't claim they're consistent. But their replies to me has been consistent at least.
Probably the company most people have had any sort of consistency from would be Stripe I think. Of course, there are cases where they haven't been great, but if you ask me for a company with the best tech support, Stripe comes to mind first.
I'm not sure it's active anymore, but there used to be a somewhat hidden and unofficial support channel in #stripe@freenode back in the day, where a bunch of Stripe developers hanged out and helped users in an in-official capacity. That channel was a godsend more than once.
