I would say any and all conversations where there is a level of disagreement are the hardest ones to have. So you name it, if both spouses are not on the same page, there's bound to be conflict. However, if those conversations don't take place, they can cause things to fester, causing unnecessary grief, until ultimately they end in divorce. In the meantime, there's potential for ongoing frustration, unhappiness and suffering.
So, the question becomes how to deal with those kinds of conversations?
—Prioritize. Taking a look at which topics are probably the most benign and therefore easier to resolve and starting there is helpful. It might mean not dealing with bigger things in the interim, but as a foundation for understanding and trust is developed, it's possible that the other topics become more approachable with time.
—Reminders of why people got married in the first place. If those reasons are still intact, then the difference of opinions need to be put into that context, and seen through that perspective. If things have significantly changed, as they so often do, then maybe the problem isn't so much the differences in opinions as they are the differences in growing apart, having different goals, wants and desires. Those will be at the core of what will need to be addressed.
—Patience. Sometimes it's easy to give up rather than keep working at things. Irreconcilable differences are often stated for reasons why couples get divorced, but you've got to wonder just how many times that's truly the case. How much was actually discussed? How hard did both parties work at it? Or did they just let things go to the point where being together was more painful than being apart? Sometimes it takes weathering life's storms in order to see what you're both capable of doing as a couple. Life is filled with hurdles, obstacles, and problems. Taking a deep breath and taking on these situational issues is going to take time.
—Agree to disagree. We hear that a lot anymore, and maybe it goes too far, because some disagreements are just incompatible, or untenable, but before that, there's a lot of ground to cover. Sometimes putting things aside to allow both parties to think about what's been said and what their true position is on things is best. So, once a conversation has started, but resolution isn't there, walking away from it for a while but still carrying on with everything else might help give each other enough space to be able to readdress it at a future time.
—Most things can be overcome if both spouses are willing. Don't give up on each other at the first sign of trouble, or the second, or the third. There's going to be more disagreeing for a while, especially in the beginning and probably years down the road. It can get better, though, if the lines of communication remain open. Some things, if not rushed, will end up resolving themselves. Others will take work. Don't expect things to be rosey all the time, but don't get down on everything, either. Marriages don't last because thorny subjects are never addressed, but neither do they last because nerves are constantly being stomped on. Somewhere, there is a happy medium, and there needs to be sufficient trust to find it.