jack and irina are most definitely first. it's just that, because of their characters, when they are in a relationship, it's not the main focus. i hate it when romantic relationships are the main focus. jack and irina's relationship is their past. it's all of the conflicting emotions. it's great. i mean, sydney and sark are second and again, it's just because i love how they antagonise each other.
2.) Irina and Jack- Despite everything that's happened, these 2 are perfect for each other! They had Sydney and were married, and I think are a great couple.
3.) Nadia and Weiss- Weiss needs a little spy luvin' in his life. Who better to give it to him then the Super Spy Sydney Bristow's sister?