Both are great pieces, but the 5990 is unique in that it’s the only watch Patek manufactures with that movement - travel time, chrono, date.
Most other Patek references use movements from one watch to another, but the 5990 movement solely for the 5990
That makes it an important piece, and also more rare. Patek just does not make a lot of them.
Also, being in steel, a nautilus, also adds to the rarity. So from a collectors perspective, think it’s the way to go
Now, and ultimately, go with which one you love more! It’s all about that at the end of the day. 