Crank scrappers work. Windage trays also work. Given the choice I'd use both. If I had to pick only one or the other, depends on the oil pan it's in. Something deeper than stock that's already keeping oil down away from the crank I'd pick the scrapper. Stockish pan I'd pick the windage tray to help keep the oil in sump off the crank. Keep in mind, a moving car moves the oil around in the pan a lot without baffles/gates etc. They're both pretty cheap insurance for your oiling system and thereby entire engine. Both are proven to add at least a little power in almost every application ever. I don't see any reason to only do one unless it's a super-duper budget or stock rebuild? There's way worse ways to spend that amount of money in a shortblock.