I usually cook for 2-3 people, but I plan to cook big pots with the dutch oven that I can get a few days of leftovers out of. I also plan to use it to bake bread and fry. Any recommendations on size?
I can't speak to the bread or frying issues, but I have a 4 qt Le Creuset and a 6 qt off brand. I cook for 1-2, but really 4 because I like several meals to freeze. I can't imagine ever wishing I had a 7.5 qt. They work best when you use appropriate amounts of food. Personally, I'd go with the 6 qt, but maybe others will have good reason for you to purchase the 7.5.
One day you will glad you bought the bigger one.
How strong is your back? (They're really heavy) I mostly only cook for two also, so the 6 quart works for me, but if you see yourself making soup or stew for a crowd, and you can lift the damn thing, go for it.
I have the larger size, and I love it. I make jam without worrying about boil overs, and it's nice to make a pot roast, brisket, or 7 stuffed peppers that I can eat for a few days, and then freeze the rest. It's a great size for leftovers.
There are only three in my family, but I love the biggest size Le Creuset French oven. I make large amounts and freeze them. I'd rather have too much space than too little. If your budget permits, you might consider the larger ovens.
I'd go larger if you're going to bake bread in it. Also a braise is a great way to feed a crowd inexpensively, and it's a pain to break up this type of cooking into multiple pots.
You didn't specify a brand of dutch oven you're considering... however, I usually recommend buying the largest you can afford money-and space-wise. I generally cook for two or three, but I'm really glad to have several large pots for when I need a lot of room or am cooking for a crowd. I think I'd start with the 7.5. If you find it's too big, you can get a smaller one later.
I have a 7.5qt and I just cook for 2 people (plus a 3 year old but I won't count him because he goes on frequent hunger strikes) and I use it all the time. I do tend to cook large batches of things so I can have leftovers though. I would always rather use a pot that is a little big rather than try to fit everything in a smaller pot.
I vote larger too! I have a whole rabbit in a single layer in mine right now and that makes me happy. Also perfect for Jim Lahey's (almost) no-knead bread. And ribs, and well I use it for about everything.
My mother in law spoils me. My birthday is Christmas Eve and for a few years in a row I got Dutch ovens. Then le crueset skillets. I have 4, 6 and 7.5. I find myself using the 7.5 the most. I just love the thing.
Thanks for the responses everyone. This is my first time posting a question and your feedback has been really helpful. Looks like I'll probably buy the larger size.