I prefer using vimdiff or gvimdiff to view differences between files. When researching ways to allow using vimdiff to view subversion differences, I came across this article.
The bottom line is that subversion passes the two relevant arguments as the 6th and 7th arguments, so the following shell script wrapper does the trick:
#!/bin/sh
/usr/bin/gvimdiff ${6} ${7}
Save the script as gvimdiff_wrapper.sh, make it executable and accessible on your path. Then modify $HOME/.subversion/config to have the following line:
diff-cmd = gvimdiff_wrapper.sh
That will allow you to use gvimdiff to display the diff generated by svn diff my_file.txt
