I can honestly say that I think I would just sit back and watch the show. We all know that there are valid reasons not to shoot either deer and those reasons are only meaningful to the hunter making the decision at the time. I have never had a deer mounted but have done a couple of antler plaques so the 170 probably would not be much of an attraction for that reason. I have seen a couple of really old bucks over the years and they are truly unique in today's hunting woods. Several years ago my son shot a very old buck during the 1st shotgun season. He was laying in a brush pile and Son literally almost stepped on him before he jumped. The first shot knocked him down but then he got back up and Son shot him twice more. We found latter that that first shot hit the right antler and broke off about half of it. This buck had almost no teeth left, the classic roman nose, and the horns were even grayer than his hide and very brittle. We didn't think he would have ever seen another spring and while maybe not actual trophy status certainly gave a teenage boy some thing to talk about for a few years.
For my own reasons I would let both walk, but certainly respect any one else's reason for taking one or the other. I would want the younger buck to remain in the woods propagating more like him in future generations knowing that life must continue onward. I would want the old one to have what ever and as much time as is left to him, maybe because I am reaching that time in my life and hope that others will allow me that same thing.