I've been to Bogota numerous times, always for work though. Honestly, I'm not a big fan. The weather's not great -- often chilly and rainy -- and the traffic is absolutely horrendous. I've never been there as a tourist, though, so maybe that's a better experience.
I strongly prefer Medellin. It's a lot prettier and the weather is much, much better. If I were going to spend a week in a Colombian city, I'd choose Medellin over Bogota in a heartbeat.