...from ESPN
Sean Payton's simple metric is: (# of sacks + # of INTs + # of fumbles)/# of pass attempts
The lower the quotient, the better.
Tracking the number of times a QB is sacked or throws a pick is pretty easy. You can get season and career stats from ESPN for that. # of fumbles lost might be equally easy to get, but fumbles not lost might be harder to get.
But I think that # of sacks avoided would be important to know.
For example, a QB who gets sacked 50 times and avoids 10 sacks is not as impressive as a QB who gets sacked 50 times and avoids 50 other sacks. The OL of the 1st QB only allowed 60 potential sacks, but the OL of the 2nd QB allowed 100 potential sacks...I'd conclude that OL 1 > OL 2, all other things being equal.
Give me a QB capable of eluding 50% of every sack vs. one who only eludes 17% of possible sacks...again, all other things being equal.