vimdiff is fantastic. Follow these instructions to make subversion use vimdiff when you run
Get this diffwrap.sh script and save it anywhere. I saved mine in my $HOME/bin directory. Make sure to make it executable! I’m showing it below:
# Configure your favorite diff program here.
# Subversion provides the paths we need as the sixth and seventh
# Call the diff command (change the following line to make sense for
# your merge program).
$DIFF $LEFT $RIGHT
# Return an errorcode of 0 if no differences were detected, 1 if some were.
# Any other errorcode will be treated as fatal.
Then change your $HOME/.subversion/config file to point at that script:
diff-cmd = /home/matt/bin/diffwrap.sh
Then go diff a file!
See this section of the svn book for all the details.