Navigon has a better looking map set has more information shown on the screen. Navigon also has the red light camera feature which is a must have in Texas. Is it worth the money? I can't answer that one for you.
I was paying $99 a year for TeleNav on my Treo Pro. It was well worth it. I have used Nokia Maps for about a year and a half now in both the U.S. and France. It's outstanding. Both have a scout function built in that works well.
I dont know about the trial.... I do have Garmin Street Pilot its a nice app I use the Flight tracker when I travel. I dont like the way it handles the GPS (The car turns in circles when you are stopped) and I think Navegon does a better job of destination mapping and rerouting for traffic etc. Garmin does show your location as a real car looks like a bad rendition of a Lotus...lol