Last week there was some analysis of how various tools did during particular merge operations (especially cherry-pick). I got the word back from one of the people in that effort that my personal favorite 3-way merge tool (KDiff3) did quite horribly. Being shocked and awed by such a statement, I decided to investigate it to see what the problem was.
Turns out, it was PEBKAC, but an understandable one - the KDiff3 docs aren't incredibly specific about which parameters are which (IMHO, they should explain each parameter is WRT the 3-way merge scenario), and the user configuring it as the merge tool got some of the arguments in the wrong order. This happened not to totally break the scenario, but it did result in the tool doing the "wrong thing".
To try and keep this from happening again, I've started an article where I'll track the correct command/argument values to use when configuring various tools for use by Team Foundation's compare and (content) merge operations.
If you have a favorite diff or merge tool not already listed and you've configured it successfully and are happy with the results, please contact me and let me know about it so I can add it to the tables.