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.
Schlecht Hatchery - 88 cents apiece for straight run and shipping is reasonable as well. They're a small, family owned hatchery, and I was very happy with their service and birds. I ordered 20, received 27 - one was dead upon arrival, and another was lame on arrival and died soon afterwards - but still have 25. They're 6 1/2 weeks old now and haven't lost a single one other than those first 2. http://www.schlechthatchery.com
After researching, we decided to use Welp Hatchery for our first (and so far only) batch of Cornish X. We just butchered half of them today. I was really impressed at how well they grew out. We bought 50, and they sent 53, 2 DOA. They were very hardy, with us losing only one (which was from my little brother handling it too roughly at 6.5 weeks old). We've read that it's normal to lose some to various fast-growth issues, but these did very well. Usually when we raise a batch of chicks we lose a few early on, but that didn't happen this time. We got 50 sexed males for $1.55/each including shipping.
i am a first time meatie raiser... just purchased 25 CX from McMurray. Rec'd 27, all very alert and alive and in good form. I am going on 10 days, have not lost any thus far.
I have no say in 'who' is the best to buy from since this is my first experience, but felt it necessary to say, that I could not be happier w the chicks i got and how healthy they seem to be. They have already doubled in size at 10 days.