We use morpheme:connect (mcn) on SWTOR. Unfortunately we also use a really old version (1.3.6), but I can give some objective opinions.
We do things with mcn that nm (Natural Motion) never intended. Literally, they came here to help us and just shrugged. We are doing things no one else is doing, so it made doing those things that much more difficult. That said, we have been able to do those things, so that says something for their software.
We've done heavy customization on the runtime, so I don't know how valuable our feedback would be. But they give you the source to the runtime, so you can do those customizations- that's another good thing. The mcn source is not available, though, so for tools you are dependent upon nm. That said, the tool has improved incredibly and they are in version 3+, so you should be fine there. We've been able to do everything we need automation-wise with the limited lua scripting support in 1.3.6, but we have a lot of pipeline code that works outside of lua (which is good- we don't want lua code to do any pipelien stuff, just manipulate the network).
The .mcn file is xml, so we are able to parse info from it without opening up the tool, which is vital. If it were binary, I'd take back every good thing I've said about mcn.
We have systems where we procedurally create networks, etc., so it is pretty customizable and robust.
Our artists and designers are able to use it, even in our complex system, so that is another plus. It really is pretty easy to use and understand.
The biggest problem we had was, morpheme by default only allows one network per character. We created a way to swap networks on the fly. Once we solved this, things got significantly simpler- but we had to do all the work for this, morpheme doesn't support it by default, and it wasn't trivial (though it wasn't too difficult either).
At last years GDC we discussed these two and the consensus was, mcn is easier to use and more friendly to content creators, while havok is more powerful and customizable- though I don't know if that's truly accurate. They're both good software from good companies. EA doesn't have a good relationship with Havok so don't get a chance to try their stuff.
So I can't speak to Havok, but I can say that I wouldn't hesitate to use morpheme again (a newer version). I'm sure my coworkers would tell you some more negative stories but, a lot of our problems are their fault- we used the tool and approached our requirements naively. Once we realized we needed to split up networks, and provide more tools and pipeline support, we were much better able to leverage it's power and not get bit by its age.