I've never sewn underwear before. But having followed the very informative and simple BusinkaMania video tutorial, practicing on a remnant of cotton jersey and I've made my first pair of knickers which fit and are very comfy. I would recommend this pattern.
I really love the variety on businkamania site. Plenty of patterns to choose from. The patterns are beautiful and simple to put together. To make the process easier, there's a YouTube channel to help, which can make it simpler for newer sewist.