There are a few beauty products we simply cannot live without: detoxifying masks (especially after a long night), handy multi-taskers , and, of course, a killer moisturizer . We've discovered pretty great drugstore options for most of those categories — but is it just us or are serums extremely hard to find at an affordable price point? In an effort to snag one that actually performs, we turned to our friends at Rank & Style to give us the lowdown on what to look for on our next shopping trip.The site uses customer reviews, editors' picks, and overall buzz to figure out which products are going to work the hardest for you. (Consider its authors beauty lovers with a penchant for math.) After crunching the numbers, Rank & Style has named Olay Regenerist Regenerating Serum the winner for its rave online reviews, as well as its popularity among editors and consumers alike.On Ulta , user Bailey wrote, "I was without this product for a week and I could definitely tell a difference in my skin when I wasn't using it, and it wasn't a good difference. This stuff makes my face feel so smooth and look bright when I use it twice a day. I'll never go without it again!"Given how much I love the Olay Regenerist line, it's pretty crazy I'd never given its serum a test drive. After trying it for a few weeks, I agree. It's a winner. This baby hydrates so well (thanks to glycerin and niacinamide) that I sometimes forget to rub on moisturizer after applying it. Who knows? It just might fall into that multi-tasking category for me soon.Regenerist Regenerating Serum, $17.59, available at Ulta