Having a good discussion about the best/most valuable modern set in ten years is awesome, but, having a good discussion about the best semi vintage set is even better! (Maybe).
So, modern sets would be Sun & Moon - Scarlet Violet. Vintage is everything from Base Set up to Diamond & Pearl (because these sets are close to 20 years old and command prices of 10k or more).
The focus, then, is on the ´in between sets´; Black & White - XY. These sets are still semi affordable (to stick with the semi theme), but are getting more expensive.
I´m gonna go with Ancient Origins. This set has been climbing fast lately, and I can see why. The three Hoenn legendary cards are beautiful and so is the box-art. Let´s also not forget that his is, again, a Rayquaza set. Although there are some very interesting Black & White sets (like Dragons Exalted), I think this set has the highest ceiling.