Can anyone tell me the big difference between the two other than about $250 dollars. I want to get a gps with a large screen and the 176 seems to be the best buy.

176C is older tech and doesn't do custom line types. Custom line types is what enables RWS/GPSSledMaps/VVMapping to make the trail some other color than red.
For example on my maps, the sled trail by default is thick yellow with orange borders. With the 176C it will show as a thick red line instead.

I have a 176c but I am going to upgrade to the 276c. In some conditions, the screen on the 176 is very difficult to read. The 276 will also give voice directions when using some of the map sets in your vehicle. The 276 will be a better choice.

Have been using both this year the 276c is alot easier to see the trails on. The 176c the major roads are red and the trails are red makes it real hard to find the trail when you want to. I was trying to figure out how to change the road color but have not figured it out on the 176c yet.