I've had five Dahua cameras for a couple of months now, and a Hik camera for about a year.
I've had no stability issues with either in terms of firmware updates.
Granted, my Dahua cameras are a newer-ish model (the Starlight 5231 turret), but I think they've released at least three firmware updates for it over the past few months. That's more than I was expecting.
I thought I read somewhere on here where if you are running a Hikvison with a really old firmware, you're expected to upgrade to all of the missing updates in-between... you can't just jump from really old firmware to current firmware. If that's true, that' kind of sucks.
There also seems to be far less confusion/concern about if a Dahua firmware upgrade will brick the camera due to regions being off (i.e. Chinese camera vs International firmware). I'm not sure if that's because most folks here are buying the International versions of Dahua firmware, or if you try to put International firmware on a Chinese-market Dahua camera, it doesn't brick it.