At the start of quick matches I often tend to end up in (partial) team fights trying to score a kill. This can take quite some time, during which you might also be able to soak some lane XP. At some point you have to decide if you'll stay to help fight, or if you should go to the lanes.
In some specific cases it looks like I can safely leave the ongoing team fight, knowing that
N of my teammates can keep
N + 1 opponents busy without a kill being more likely on either side. I could stay, but I don't give a really big advantage to my team. So I have to weigh the value of my hero being there against going to a lane.
All this is just context, and my question is about the numbers (and ignoring more subtle effects such as creep equilibrium, time to run back to the lane for a killed hero, etc): how much XP is a hero kill worth, relative to creep kill? And is there a difference between low and high level?