How might I compare the general stability and ratings of corporate and gov't bonds

How might I compare the general stability and ratings of corporate and gov’t bonds overall? I don’t know much about this subject, so I’m not sure of the metrics I should use to examine this issue, especially over the aggregate (or an aggregate of highly traded bonds). Any help?

A good indicator is the interest rate that it pays. A US Treasury bond is considered default proof and since it is the very safest investment you could possibly have, it pays the lowest interest rate. Reputable companies pay a few points higher because, while unlikely, they could default on their bonds. Then you get into below investment grade or “junk bonds” that pay even higher interest because of the high risk.

The market is generally pretty good about demanding an interest rate that accurately reflects the risk/reward.