I've been trying to use ntop at my organization for a while and have had nothing but problems with it. The system I run it on is a fairly vanilla Redhat 5 system (Sun X4140) and ntop seems to run for a couple of days and then crashes. We've had to script automatic restarts of ntop, but when the crashes combine with the fact that ntop doesn't persist most of its metrics it becomes a dealbreaker for us.
What are the big competitors for ntop? I've played with a few of the other open source tools, and most seem to not match the features (and the majority seem to have not been updated in a long time). Are there any commercial replacements for ntop, or even hardware devices that can provide the same functionality?