Cows drop from a special TC, and can drop any white (very low odds for the TC87 items) or set. Flayers can't drop TC87. Try area lvl 85 areas, these have monsters that drop much better than cows, and the exp is better.
i have found that even doing stonefield area is quite profitable (need to get leg after all) as there are usually large groups of carvers hanging around in their camps. but yes if u are after elite white items then try the pits
It helps if you state which elites you're most hoping to find. Cows have the best chance at dropping Sacred Targes which are bank since they have the highest block percentage of all pally shields and can have up to 45% resists to all. Since there are now very popular 3 and 4 socket shield rune words, you can get some nice jink with a 30+ resist all STs and Smiters love the 40-65% ED ones. Hell Cows also have the best shot of dropping Monarch Shields, Dusk Shrouds, Cryptic Axes, Great Bows, and Collossus Swords (although I'm not sure the CSes are in great demand nowadays). The Monarchs alone are worth it. Every time you find an unsocketed or 4 socket Monarch, you just earned yourself a Pul on USWest.
The Pit looks pretty ideal for finding those Berserker Axes, Collossus Blades, Bone Visages, and Archon Plate. Although I'm starting to warm up to Maggot's Lair as well. There's a lot of monsters in there and they all drop high. A pain for some builds but a pretty easy run for others.