A badly scratched and number engraved Model 19 MAY not ever be considered a collector's piece. However, model 19's are highly sought after - so the 19 in question may well end up, in the future, being a lot more valuable than the Ruger (which has no real collector value). S&W's almost always have better trigger feel than DA Rugers. If in good mechanical condition, the 19 very likely would be the better shooter (though only because of the trigger).
The Ruger, if you are considering the purchase as a gun to SHOOT and CARRY, may be the better prospect. It is a more modern design, very robust and reliable, a bit smaller than the 19 and lighter.
If it were me (and I have both S&W's and Rugers - and I carry an SP101 every day).... if the gun was to be primarily for SD, carry, etc. ...I'd get the Ruger. IF future value was an important part of it - depending on how badly damaged is the finish on the 19 really is - I might well get the model 19.
The crane issue with the 19 is probably a missing or damaged crane screw - easily replaced. But, I would check this closely. Worse case, the crane is damaged or broken. It can be replaced with a used one fairly cheaply (and does not require a gunsmith), but availability might be an issue. I would also consider WHY the crane comes off - I would have a close look at it and the screw (if present) - before I would make a final decision.