A little browsing in the meat section will reveal that there is no best cornish cross, because they vary from year to year. This is because they are a cross bred bird, and the process of breeding for fast growth, etc. is an ongoing one; they never end up with a final product in the sense of not needing further cross breeding.
Price will vary a little, but the biggest factor is shipping. Probably the best way to save money from most any hatchery is by ordering a larger number of them, then splitting the order with neighbors.