there are several pros and cons with both...
Rx350
Pros: better gas mileage, feels more "handy" for city use especially if you live or drive around in a more crowded city, has HIDs available if you wish, has a optional power rear door which people prefer over the Gx's sode opening door.
Cons: personally the design for me how they tried to make it a crossover suv, a lot of blindspots when u drive it, due to their crossover design, no 3rd row seat option if you need it, smaller space inside compared to the GX.
Gx470
Pros: more truck-like size w/o the rough ride/bounce of a truck, tows more than the Rx350, more interior space, has available 3rd row seat,better design for me at least, and has really good off-road capabilities w/o compromising the smooth ride while off-roading
Cons: side opening rear door, no HIDs avail even as an option, a lot worse on gas mileage than the Rx
Hope that helps!!