The problem is that we've had media saying it's one thing or another. I think it can be both.
There was spore delivery as far back as Gibson's Alien 3. Not to mention, I never understood how an egg implanted in the esophagus winds up in the side of the chest. It would either go into the stomach or the lungs. And that would create noticeable distress. Although the stomach may work from a parasitic standpoint. The victim wakes up thirsty and starving, and unknowingly feeds the embryo by consuming large amounts of nutrition.
Resurrection of course, showed the chestburster climbing up through the esophagus. But it's resurrection, so you know, grain of salt. Spores would allow the alien tissue to pass through human biological structures, like we saw with ledward. As a method of delivery, it's superior. But I still think there's room for both direct embryo/egg implantation and spore delivery. Just like there's regular and queen facehuggers. The sneaky little b@$tards are just full of surprises. And I think possibly capable of being able to determine the method of delivery, given the particular circumstances and needs of the species.