WinMerge is better. It has better UI: bottom line comparison, keyboard shortcuts, copy left to right and vice-versa, lots of preferences settings, etc. Too bad it is Windows-only.
If you can accept a paid version of WinMerge for Linux and Mac I'd highly recommend BeyondCompare (U$ 30.00).
If you can accept a paid version of WinMerge for Linux and Mac I'd highly recommend BeyondCompare (U$ 30.00).