When I bottle I just do 4 12oz for carb sampling. the rest are 24 or 36.
If the beers not a keeper then there's no reason you can't go for large soda bottles.
I like to use brown 1 quart PET's. They make bottling quick and easy. No scrubbing is required, ever. Not to mention I can tell SWBO that I'm only having one!!
To me they are the perfect size. Usually I split one with someone or have two 16 ouncers in my favorite mug. If I used gallon jug I would either waste it or be drinking flat beer.
They also take up less space in the fridge, until just recently I had 18 gallons in my beer fridge.
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I usually do a split...one or two 2-liter bottles, a few 22s, and the rest in 12s. Although, I did take my first crack at a Belgian recently and bottled that all in 750ml bottles for nostalgic purposes, but that was just last week. I have lots of different bottles on hand, so I can decide what I want to do. I bought a couple of Grolsch-style flip-tops at a local kitchen supply place, look to be in the 24 oz range, and tried one out. It survived a month of pressure, so it's a viable bottle, but at $3.99 per bottle, it might be cheaper to buy then with the Grolsch in them!
There are plenty of sources for 1/2 gallon growlers, but getting them to hold pressure is tricky. Two and three liter soda bottles work fine, you just have to keep them in the dark to avoid skunking.
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Did you have some that you want to use, or were you looking to get some?
1 gallon jugs make good small-batch primaries / secondaries. I am looking for some (without paying $4-5 at LHBS) to do some small or split batch experimentation with different hops, fruits, flavorings, etc. If you have them, use them for that, otherwise, the plastic soda bottles work great and are cheap, just keep out of light and drink within about 3-4 months.