What would folks suggest for a merge tool?

Our project is in C#(XNA). We're using Mercurial and interfacing with it via TortoiseHG. Occasionally I have a lot of work to do helping the merge tool make decisions, and even then sometimes I get it wrong. I know I have two tools at my disposal, though so far I have only used Kdiff3 (just trying to reduce time spent learning different interfaces). Sometimes kdiff3 can't tell that my partner and I added things to the same spot and that we need both. (I haven't been able to find a "keep both" command during the merge process.)

Or maybe I'm just Doing It Wrong. But I'd like to hear thoughts on merge tools.

I agree with frob, Araxis is by the far the best. And also the most expensive.

For a cheaper option, I would go with BeyondCompare.

I'm pretty sure the perforce merge tool is free to download on its own - P4merge. I have never had any problems with this and for c# files should be more than adequate. That's what I would go for if you want a free solution.

Another vote for P4Merge from me. Though I've only ever used one other merge tool, this has the advantage of being free (within requirements). :)

You can view the original file(base), and branched versions(yours and your partners changes) for resolving conflicts - and specify which change should be used(or both), and also, if necessary, modify the result by hand in the merge window below.

(It also works for images too, and can highlight the differences.)

WinMerge is free, can be configured to work with Tortoise as default diff/merge tool. I've been using it for more than 5 years now, it never let me down. It also has folder compare like other paid software do.