Phenom_85
Erailea
depends on what you're doing. If you're looking to build a deck from scratch buying packs is probably better because you'll get wads of cards to choose from / use. You might even get the rarer cards you wanted or didn't know existed in the process
If you're looking to finish a deck with a small number of very specific cards, buying individually is probably better depending on the rarity of the card(s) you are looking for.
tipped for being so true
if you're just starting out, buy a starter deck (or preconstructed deck) and some booster packs. However, if you're collecting and just need those last few cards to complete the set, then just buy them from a store that sells them or buy online (but be careful on that end)
If you're going to buy cards individually, you're better off buying them online from somewhere that is reputable. Most stores that sell cards individually are trying to support their store, rent, utilities and things like that. It wouldn't surprise me if you would pay more in a brick and mortar store to get something you could get online for a bit less.