D.D.
I did combinations of 2 oz and 4 oz for freezing. I usually used the 4 oz - 4 oz was the most either of my kids ever took in a bottle. And I used the 2 oz ones later to top off fresh bottles when I wasn't pumping as much in the later months. Daycare also kept a few 2 oz ones in their freezer in case the baby had a hungier-than-usual day.
Oh, and you didn't ask this, but this is the best freezing advice I got: use the plastic bags, put the milk in, label, and freeze flat. Then get a plastic shoebox and put in the freezer. You can put all the flat milk bags in like cards in date order - always just put new ones at the back. Then it's easy to find the oldest ones to use first - just use from the front. I started pumping once per day right from the beginning with my second, in addition to exclusively nursing, and it was a Godsend when I had been back at work for 8+ months, it was getting harder to pump enough, and I had a great freezer stash to go back to.