To compare files I used to be very blunt and use
diff $file1 $file2
but then my front-desk mate said "Add | vimdiff - ". He has shared some ideas on how to compare stuff with another colleague of ours.
In the meantime, my boss introduced me to tkdiff and I absolutely loved it.
As a good open source software ;) works on Linux, Mac and M$ Window$ :)
So enjoy!