80% lowers are a good "to-do" project but not cost effective. Do you need a lower without a serial number? 80% lower and cost of jig, plus drill bits, end mill bits and drill press/mill equals a bunch of money you can put towards more lowers or go-fast parts for your rifle.
Some people prefer billet, some prefer forged, I prefer billet - don't know why, probably the way they look, who knows?