Looking to buy a dutch oven what size for lg egg

I have the Lodge Logic™ 9 Quart Cast Iron Dutch Oven but I like to cook big pots of chili for a couple of weeks of frozen lunches. I will, however, probably buy a smaller one for smaller meals for the family. So really, it all depends on how you're planning to use one.

Your not really limited with size of DO to fit in the large, for the most part. As noted above, both 5 & 9qt units are used regularly, and quite probably could go even bigger. 5qt is very common, and will even fit on the Small Egg. I have a 2, 5, & 7qt....and use them all.

Note the wire bail handled units enable one handed carrying, and are very nice although slightly more difficult to clean.

I like my 3.5 quart oval DO, as the curved shape allows it to tuck into the edges of the BGE. I have every size imaginable from 2 cup (yes, I use it) up to 9 quart.

the other decision you need to make is whether or not you buy a conventional flat bottom oven or a camp style one that has 3 legs. Personally I like the camp style when used with the inverted plate setter in that the space allows heat circulation and IMO cooks better. OTOH if I'm making something whereby I'll be taking the oven somewhere like a potluck and I will be using a hotplate to keep it warm then I use my flat bottom oven.