Evaluating strength is a tough dilemma. One measure might be to consider if the program will enable you to accomplish your career goals. For example, I want to be a cardiologist, so I am looking at programs that place a lot of fellows in cardiology. However, this information isn't always readily available...
Some other resources for researching residency programs:
US News and World Report Hospital Rankings. Not really sure what to make of this. But since I'm interested in cardiology, I looked at which hospitals ranked well on USews in cardiovascular medicine.
scutwork.com was initially promising, but most of the entries are old, and almost all the entries are positive, making it hard to discern which are truly good.
The residency program's website. I try to pay attention to the more objective information if possible since they all try to sell themselves. If you're interested in global health for example, finding out if they have a global health track would be helpful.
FREIDA. Most of the info here doesn't seem to tell you what it "feels like" to be a resident at a given program. However, it does give you some important info. For example, for the IM programs I am considering, I found out the number of lecture-hours per week (objective measure for emphasis on education), the % of time spent in an outpatient setting (important if you are a primary care guy), how often you take call at that program, and last but not least, how much vacation time off you get.
None of these really tell you what it's like to be a resident at a given program, however. Are there any resources I am missing?