Oranges have been some of the most inconsistent fruit for me tbh. A good orange is great, but it's just as likely to be tasteless or sour. I do live far from orange farms though, so that's probably the issue.
Grapefruits are actually tasty and easy, you just have to do it right: Cut in half so that you slice all the segments, pour sugar over the cuts, then use a tea spoon, the more acute the tip is the better. They're still tart but it's the right kind of tartness.