Yeah, I spent money on both and got to compare them. I'll list some pros and cons for each app, those will be stuff that the other app doesn't have or does worse or better.
- I had Navigon as soon as it came out, you probably remember how TomTom kept stalling its release. Navigon is feature rich, and I love it.
--- Pricing (the live traffic option and panorama 3D are one-time lifetime subscriptions). I haven't taken advantage of its region apps since I already had the all-in-one.
--- Features: I love how it shows the speed limit of the road you're on, especially when you see that HP in the distance. Also the lane assist when exiting a freeway is awesomely handy.
--- It's slow to load, definitely not something you want to access quickly, iPod control from within the app is horrible. The workaround is to start playing the iPod before starting the app and controlling the iPod from some remote.
- I tried TomTom because I got tired of Navigon crashing occasionally and its slow slow start ups.
--- It starts wicked fast, definitely something you can and want to quickly consult. Also, switching to options within the app is fast and not annoying.
--- It has more voices to choose from, though that is not an issue with Navigon.
--- It seems to do a better job guessing where you are if the GPS information is a bit off, Navigon easily goes all over the place.
--- Pricing: The traffic option is a yearly subscription.
--- It's not as feature rich, I miss the lane assist and the speed limits but I gladly do without those considering how fast it starts up.
For usability I always fire up TomTom since Navigon takes too long. But for long trips I sometimes stick to Navigon, since its features are fun. But I frequently decline incoming calls when using navigon, especially when there's a lot of switching roads ahead. It seems that this is something Navigon _can_ fix since, well, TomTom did it. But it also seems they don't want to invest resources in that and expect you to fork out the $$ for a better phone.