things i consider essential when looking at programs:
1) will i come out well trained? to answer this i look at the case numbers and resident autonomy, as well as didactics and surgical skills training. ask the upper years if they feel prepared for going out in the real world. also, strong minimally invasive training is essential.
2) how happy are the residents? i have found that residents feel happy if they are feel important, and that the hours they work and learn are well spent. if it is a supportive environment, even busy residents seem happy. and, i plan to spend 4 years in this program, and i am not willing to sacrafice my personal happiness for training.
3) will the program get you where you are going? i like to keep in mind that even though i am not currently interested in a fellowship, i should still keep the door open a little bit. it is tough to imagine now what i will be doing in 4 years, and with further exposure a fellowship may turn out to be the right thing. so, keeping that option open is important, which will lead me to certain program types. consider what you think you want to do, and what you may want to do.
4) is the program ok geographically/lifestyle-wise? ask about recreation, cost of living, events outside of the program, schools, or whatever may be important to you and your family.
also, it is important to be sort of flexible with what your perceptions are. two examples...some say go to a program with night float only. this may lead you to pass over some programs with conventional call schedules that are better, and these programs may do a very good job of managing the call, giving you a better experience than night float, and keeping reasonable hours. and be flexible with geography..i recently interviewed at a place where i had never visited, and assumed would be ok at best. i loved it, nice town, great cost of living and a surprising amount of fun to be had. there are surprises out there, don't shut them out.
best of luck!