Use diff's side-by-side display option by default.

.zshrc

@@ -139,6 +139,13 @@ alias "ghc"="ghc -dynamic"
 alias "less"="less -R"
 ###
 
+### Better diff
+# Note: not an alias so that `tput cols` gets always evaluated
+diff() {
+    command diff --color=auto --side-by-side -W `tput cols` $@
+}
+###
+
 ### Colored man pages
 man() {
     LESS_TERMCAP_md=$'\e[01;31m' \