90% of all forged receivers start out the smae way in the same place. The mark of quality is in the machining, finishing and fitting of the receivers. Bushmaster, Armalite, and Rock River Arms are above and beyond the best out there right now. DPMS and Colt would be next after the first three. Olympic would follow on very closely to them (Olympic also forges and casts their own receivers).
Cast receivers are inherently not as strong as a forged receiver. Most likely you will not know the difference. There have been a few examples of cast receivers breaking apart due to bad cstings. These situations occur only in 1 out of a coupla thousand. The chances it would happen are slim. One of my AR's is cast and It has worked just fine even though I abuse it severely. It does have a rougher finish, but i am not sure if it is because it is a casting or that it just wasn't smoothed out in order to save cost and labor.
If cost is not an issue, look at Bushmaster (they are the only ones offering barrels in 4150 steel, chrome lining is standard, and standard models use 5.56mm milspec NATO chamber/match rifles will use .223) first, then Rock River (4140 barrel steel and chrome lining only offered as option on M4 type barrels). If you just want to plop down a big wad of cash, look at Armalite (4140 barrel steel, chrome lining available, however they only offer .223 chambers). All three are good they only use forged receivers, and the fit and finish is superb.