Personally I like my Columbian Wyandotte bantams over my standard size CW's. They take up less room, eat less and produce better. Their eggs are not much smaller than my standard size. However, I recently purchased 2 australorps and they are really winning me over to the "dark side".
They have been very hardy going free range and produce large delicious eggs, but I haven't had a winter with them yet to decide how well they do in our cold winter.
I love my banties. They are friendly, and easier to tame. And I can have more chickens that way. Haha.... chicken math.
However, if you are selling eggs people don't like banty eggs as much. I don't mind eating them.... you just need more.
Personally I prefer LF/Standard birds. It's all about your amount of land and your location as well as preference, but, I like "standard" sized birds better no matter my space or location, because most bantams have ugly eyes and heads in my opinion, have way too dropped of wings and short, U shaped backs which obviously says something wrong about the body, and most bantams are a miniaturized version of a normally large breed, which to me isn't entirely natural.
Um, breeds in general aren't "natural" are they, roosters in the wild dont mate with specific hens to get chicks with specfic characteristics!
I have slowly been converted to bantams for all the reasons others are stating. They make so much more sense to me from a utility stand point. And they are just all around easier to keep, and I've actually personally found them to be heartier in the ones I've had so far.
You banty fans should look up the heritage bantam thread!