The only time(s) I suggest billet over forged:
If cosmetics are really that important to you...
If the billet has integral features (ie; ambi bolt release) that are unavailable on forged receivers. (Mega, Seekins, AXTS, KAC, LWRCi)
Companies like Noveske, LMT, Mega, Colt, even new comer BAD Inc have all shown that a a high quality forged receiver can exist, and be extremely functional. If one of the above reasons doesn't apply to you, stick with the forged... Just because it's forged, don't think you're saving money. In most cases, you get what you pay for.
As for integral features, Aero Precision has even started implementing special features on their forged receivers, like the "PDQ" ambi-bolt release. No longer do the billet receivers hold a monopoly on that market.