I know that the plural of anecdotes is not data, but I currently run Sid, and I have been for several years. It hasn't been problem free, but I don't recall a system-killing update. The most common problem is some missing or broken dependencies for a package forcing me to hold off installing a package or updating my system for a few days.
In the mean time, back when I used to live with someone who used Ubuntu as his main system, and when I used to run Ubuntu on my laptop, I had to fix system-crippling bugs at least 3 times.
So, anecdotally, I've had less system-killing problems with Sid than Ubuntu's stable releases.
When it comes to system-killing bugs, it also matters whether you update daily or less often; system-killing bugs often get reported right after a mirror pulse and fixed one or two mirror pulses later (less than a day).
In the mean time, back when I used to live with someone who used Ubuntu as his main system, and when I used to run Ubuntu on my laptop, I had to fix system-crippling bugs at least 3 times.
So, anecdotally, I've had less system-killing problems with Sid than Ubuntu's stable releases.