The long-tail cast-on is my go-to cast-on. It’s firm yet elastic, and nice-looking to boot. That being said, it’s not reversible–the right side looks completely different from the wrong side. Because the right side faces you when you are casting on, it’s a good choice for working a circular piece; however, if you are working flat, you may want to work a wrong-side row as your first row. Experiment with it on your own, and you will see what I mean.
In my opinion (and from my experience), if you’re not acquainted with the long-tail cast-on (or one of its variations), you’re missing out. So, grab some needles and yarn, watch the video, and take your knitting to the next level!