Mark in Paris[Purist]
10488
I think they both have their appeal
It is another question people like to debate quite much as well.
I made a sort of comparison between the 5070 and the 5170, there is a little part on the two calibers:
www.watchprosite.com
In fact, my opinion would be there is no 1st and 2nd as they appeal for different reasons.
On the finishing level, they are around the same. The 29-535's finishing is excellent, at the level of the 27-70. The latter has a few finished inner angles while the 29-535 doesn't but this is not the main element to consider and many high-end calibers don't have inner angles either. For instance, I prefer the design of the 29-535's bridges better, but that's a matter of taste.
On the technical level, the new 29-535 is better. It has been designed by the brand's watchmakers from a blank paper (not many brands are able to do this, especially the way Patek Philipe did), taking into account many clever and often simple improvements. It is a fantastic movement.
The 27-70 has this little old charm and historical origin that makes it an important caliber from for the brand and in watch making in general. It is specific to a certain era of the brand (1986 in the 3970 to 2010 for the 5970).
I would say, if you consider getting such complication, that both choices are excellent.
Best, Mark