I am not an UML fan, but I have to use it from time to time. To create models I am using Enterprise Architect from Sparx Systems. It is not industry leading software and I think it has good  relation between value and price. It is quite complex tool with a lot of features and some of them are little bit tricky to use. Overall experience is quite good, but what I am missing is UX  strategy or concept. UI is not simple nor intuitive as many complex tools these days are. One IMHO crucial and critical issue that make me angry was toolbar especially Undo/Redo buttons. As you can see from screenshot icon usage is totally confusing. Your right brain hemisphere gained experience that icon with floppy drive represents saving to disk file. Usage of this icon in different context is more than unhappy decision. I have to say that I clicked it number of times before I remembered this “if”.