IMHO, I would take the middle ground for a 3 change system and I'll elaborate:

1- rapid rooter plug for clone or 18 Oz "Solo cup" of soil for seed.
2- 1/2 gal pot for veg
3- 3 gal pot for final veg and flower.

Just be aware not to soak the bottom of the soil every time because it will stay wet much longer. Some give "half waterings" or just a spray surface watering to compensate for a dry soil top because you don't want to soak the bottom again. I'm sure it takes getting a feel for it. Less is more.