[Mogul, XV6800 General] sadthai:
i have used iguidance, garmin xt, tomtom 6 and now tomtom 7. here is my personal opinion:

iguidance has tts(it pronouce the street name), which is a big plus. however, the routing engine is not very good. if you go an interstates trip, i dont recommend it. iguidance also has poor to average 3d views. it has very nice 2d view though. iguidance 2009 ppc with new navteq with "traffic pattern" and 3d lane changing view is coming out in august 2009.

garmin xt has nice 3d view, but the 3d autozoom zooms out way too much, specially on a long drive. if turning off autozoom, you dont get any zoom in when you about to make a turn. the gps lags quite a bit behind for me, perhaps 2 seconds behind real time. all gps navigation software lags a second behind real time, except for tomtom which predict .5 and 1 second ahead. the routing engine of of garmin xt is not so good either. i have entered several know destination of friends and families home and it never gave me an ideal route. i also tried to route from san jose, ca to falling waters, wv and it have me go down to las vegas and through interstate 40. the ideal route would be interstate 80. garmin xt does have traffic, however, from my understanding is that it doesnt update routing base on traffic info during driving. correct me if i'm wrong. garmin xt also has the best POI search engine.

tomtom 6 routing engine is not that much better. it doesnt give me the ideal route to friends and families destinations, but it did route me through i80 instead of through las vegas and i40 when i tried to route from san jose, ca to falling waters, wv. the traffic feature on tomtom6 works really good, but its not free. traffic updates continuously and update your route accordingly. i've seen traffic work again and again for me. tomtom6 also predict gps info .5 and 1 second ahead of time so you get virtually no lag, tomtom is the only software that does this. the 3d display is video smooth like and the 3d autozoom is perfect for me. the menu of tomtom is also very easy to use. you can navigate through tomtom menu with one hand, and entering destination address, it is also the easiest. some other negatives with tomtom6 is that map is outdated. you can not search any POI within a range. you have to search POI within a category and sometime the category that you want to look is not there. also the "next street" name of next turn is small and way at the bottom.

i like tomtom7 the most. most of what said above about tt6 also apply to tomtom7, but tt7 has much improved map and routing engine. it has the best routing engine by far. when entering families and friends destinations in different cities from 50 to 100 miles away, it always give me the most ideal routing. version 7 map also has mapshare which you can get map correction from thousands of other people using the same map. my g/f neighborhood in WV and my cousin address in PA are not in any of the previous navteq(2008) and teleatlas(2007) map, it is now showing up in the latest telelatlas map. in certain big cities, version 720 also offer detail information including side walk and building and house floor plan showing up as 3d shaped that resemble the floor plan of the particular place. it even has my neighbor's swimming pool. the down points of tt7 is that it does not offer text to speech, and like tt6, the POI search sucks.

i highly recommend tt7. i think the most important feature of a gps navigation software is its map and routing engine. you can download tt7 from this forum and buy the version 7.20 north america 2gb map for about 70 bucks, and you are good to go.