Myself & 2 friends recently watched through all 12 films in the franchise. When done, we decided to rank 'em. In lieu of starting a new thread or replying to threads that are 10 yrs old based on "search" I'll just dropped the lists here. Seems appropriate enough.
Mine
1. Alien
2. Aliens
3. Predator
4. Alien 3 (Assembly Cut)
5. Prometheus
6. Predator 2
7. Alien vs. Predator
8. Alien Covenant
9. Predators
10. Alien Resurrection
11. The Predator
12. AVPR
Friend A
1. Alien
2. Aliens
3. Predator
4. Prometheus
5. Alien Covenant
6. Predator 2
7. Alien 3
8. Alien Resurrection
9. Alien vs. Predator
10. Predators
11. AVPR
12. The Predator
Friend B
1. Alien
2. Aliens
3. Predator
4. Prometheus
5. Alien vs. Predator
6. Predator 2
7. Alien Covenant
8. Alien 3
9. Predators
10. Alien Resurrection
11. The Predator
12. AVPR
All 3 of us had the same top 3 but conceded they're essentially equal. I would give any of them the top score of whatever particular rating system was being used. I do think there's more depth to both of the first Alien films, compared to Predator, but Predator does what it does so purely & perfectly. If not for the Assembly Cut of Alien 3 I'd likely have Prometheus slotted 4th & we'd all have that in common. They don't think as highly of Alien 3 as I do, it appears. We also all agreed on The Predator & AVPR being the worst of the lot, but my one friend was insistent that absurdity of Requiem amuses them compared to The Predator, why they claimed is the largest disappoint of the series. The middle is a jumble, but that's to be expected. Good discussion ensued.