I've been a longtime fan of biking, I guess it was unavoidable considering how much my dad loves it. I love how fast it gets you to the places you want to go. I used to bike down along the hudson so that I could eat lunch downtown and shop. Biking is tailored to your level of proficiency, which is why it's an easy sport to pick up. If you want to go all Lance Armstrong you can participate in races and long distance cycing, but if like me you want to cruise sometimes and work other times, its easy to just adjust your settings and pick another path.
Spin is a type of indoor biking which provides an intense workout and is tons of fun. All of my gym classes are spin classes, so I've had some experience by now. It is tons of fun and forces you to push yourself. With music on time passes super fast, I love spinning to old school hip hop, nothing like Usher, JZ, and Missy Eliott to make you work hard.
All in all, bies rock, spinning is the workout of a lifetime.