[burnblue]

I've gone through a bunch - Illustrator to Balsamiq to Mockflow and now HotGloo. I like Mockflow and HotGloo (both online fee-based apps) because they offer:

(1) Master Pages (or at least Master Objects) to keep things DRY (2) a way for clients to view, navigate, and comment directly on the frames (3) a good balance: low-fi enough to avoid seeming like a design pass, but hi-fi enough that each object is distinct and recognizable (4) a good selection of resizable, customizable widgets (5) an environment separate from the design file. Unlike many, I actually prefer to start from scratch with the design - it frees me from conforming too tightly to the frames, and leaves open the possibility for further iteration. Also, it's handy when passing frames to a visual designer - they can use whatever design tool they like.