whats the difference between a LT285/70 R17 and just a 285/70 R17?

I have a 2006 f150 stx 4x4 reg cab reg bed and do some towing every once in a while. Which one should i get.

Im going with the bridgestone dueler at revos, that should fit.

 

Looking at the Bridgestone web site, there is a P285/70R17 and an LT285/70R17 Load range D. The P is a passenger car tire that can be used on a PU due to size and load rating, although it will be at it's limits. An LT will come in 3 load ratings. C, D, and E. There are higher ratings but you would only need those on trailers or larger trucks. C would be the lowest load rating, but would be superior to a passenger car tire. D would be higher and E even higher.
What that means is that the higher the load rating, the better it can handle what you are doing with your vehicle, especially towing and load carrying. Pressures that you would run the tires at would also be different. A p series with a max of 35 psi would have to be run at 35 psi, it's max to handle the load. An LT load range C tire would be run at 40 (max 50), which would handle enything you could load into your vehicle and stay within it's ratings. Overload would require a higher pressure, probably it's max.
Also a p series would be speed rated, while an LT is not. Usual max for an LT is about 100mph.