I prefer 1 liter PET bottles because:

[laddg]

1. If I drop them they don't break
2. They are quicker to fill and cap than 12 ounce bottles
3. I can tell if carbonation is taking place by squeezing them
4. They are about the amount I drink in one evening, so they help regulate my consumption
5. I can pour a glass, and reseal it till the next one and it stays pretty fresh
6. If I over-carbonate, I can "burp" them to let a little pressure off

I'm not sure why more people don't seem to use them.
DJG

P.S. the 500ml PET bottles I normally see don't make quite as much sense to me... but I definitely like the 1 liter ones I buy for about $1.25 each

 

[shelly_belly]

My wife drinks these then I reuse the bottles. I think they are about $.68 each from walmart.