TomTom has been getting a lot of criticism for their lack of updates. Navigon has actually pushed out 4 updates in the span of a few short months while TomTom has had nil. It's one of the reasons I'm looking into Navigon as a road navigation solution myself.
This is something I plan to write about. But it's merely one company's method versus another. It's called iterative design. Where each version of an app builds on the previous version. Navigon seems to be pushing them out faster, but why is it so wrong that TomTom is taking longer? It's not that it really matters.
What SHOULD matter is which one offers what is best for what YOU want.
Want POI's? I think TomTom has Navigon beat based on user testimonials.
Want more up to date and accurate maps? I think users will also state that _mostly_ TomTom wins this as well.
Which one is better at routing? Navigon MIGHT have it won if it comes down to using Live Traffic information. Which may or may not be available for your area, and you also have to pay extra for it anyway. So without live traffic, which one is more accurate?
They both announce street names now.
Both let you control your music now.
There's a lot to choosing which one is better obviously and one person may favor features from one app over the other. I think in the end TomTom might be looked at in such a way that it seems negative. But it might have something to do with expectations and people seem to have pretty high expectations of TomTom but less so of Navigon. Which benefits Navigon obviously.
I fully suspect that most casual users will be happy with either of them. Only the hardcore users seem to be the ones complaining or saying one is better than the other. I mean, seriously, you've gotta be pretty hardcore to have purchased BOTH. That's over $200 normally priced (with Live Traffic on Navigon).