Good ol’ natural window light. It’s still my favorite.
You can set up all the fancy flashes, umbrellas, soft boxes, and fill cards you like. I’ll take light streaming in through a window seven days a week and twice on Sunday.
To me, it always represents the closest after-the-fact reproduction to what your eye is actually seeing, and it looks fantastic to boot. Oh, and did I mention it’s free, unless of course you don’t have a window. You could always ask to borrow someone else’s, so you’ve got that going for you.