I'm raising my first batch of meaties this year also and we got the Freedom Rangers based on research I did that says they are a relatively fast grower (12 wks) and range well. Yesterday they were three weeks old and we've only lost one so far (out of 26), feeding them a 20% organic grower mix all along.
Our Delaware-based mutts are great foragers. Very active. I think just about any bird (with the possible exception of some extra-lazy CX) will forage effectively if given access to good pasture. We use tractors, and our birds graze the pasture down before they have time to pave it in poo. CX seem to be best at burying the good pasture with a thick layer of manure, instead of eating any of it!
The bird that has the reputation for being the most industrious forager is the old-school Dark Cornish. There are a number of threads here on BYC on the subject, if you do a search. I've never raised them, but have been tempted to.
I tried a batch (32) of red laced white cornish. Cornish have the large breasts and are great foragers but develop more slowly than your birds designed to pack on the pounds. However, I provided less feed over the course of their lifetime (5-6 months).
I kept the two best roosters and bred them to some Egyptian Fayoumis. Trying to select for the large breast and foraging capabilities. But the RLW Cornish were very good foragers, I was pleasantly surprised.
weve only been raising broilers for six years now but here is our experience. we raise 50 to 75 broilers at a time on pasture. we usually get 8 to 10 freedom rangers or red rangers to grow with them .they seem to make /keep the white broilers very active. The whites seem to mimic the reds from day one in the brooder.we end up with very active white broilers.