My experiences with TogetherJ have been lukewarm at best - crashes often and extremely slow on a P3-600 w/128mb RAM. I haven't used Rose directly, but an architect on our team does - his impression is that it is quite a bit more robust than TJ, both in features and stability.
Personally, I've been
testing a new tool that I'm falling in love with called JaVISION from Object Insight. It certainly doesn't have the feature sets of TJ or Rose - it is primarily a class diagramming tool that has both forward and reverse engineering (no sequence diagrams). It's fast, easy to use, prints beautiful diagrams, and is what I now use when I'm starting my designing. It can automatically keep the model updated as you modify your code and has some other neat diagramming capabilities (integration with JavaDoc). Highly recommended.