Comparing apples and oranges. The 5170 is a chronograph Patek has long needed and successfully captures several facets of Patek's history in my opinion. A pure, Patek designed chronograph movement, will carve its own story in history. Although this will be produced in "limited" numbers, I imagine 000's rather than 00's will be produced. One is never sure how the diamond markers will be translated over time, a risk in my opinion. Overall a sublime "complicated" timepiece if you manage to convince your AD to sell you one.
The 5970 continues a remarkable story of PCC timepieces. Collectors are in awe of its Lumania based movement, I personally feel that a brand like Patek should never use third party movements, but must admit that it is one heck of timepiece with a beautifully balanced dial. I have recently come across reasonably priced versions, which are on par if not cheaper than the 5170 RRP. It could be a good time to buy such an iconic timepiece.
Start off by asking yourself if you want a new or used watch. If you are not bothered, I would personally opt for the 5970 as prices are currently attractive and you will get much more for your money. Economics aside, I still think the 5970 is the better offering overall, it has a long established history, solid following and compares very favourable to pre and post models.