I have an RT and have been shopping for either an F3T or "L". To me there are several major differences.
First of all, wind and weather protection. The RT has much better protection from the elements, including an electric windscreen that is adjustable. The F3 windscreen is fixed with no adjustment. The RT has more body work that protects the rider from the elements. If you like being out "there" or if you like a higher level of protection, that will lead you in one direction or another.
Then there is the riding position. The F3 has the down in it, feet forward riding position, akin to a cruiser. The RT has the more traditional riding position of being up higher/on top with the feet more underneath. People have preferences and opinions, but it's up to the rider to decide.
Maybe because you're lower and the center of gravity is lower on the F3, it feels livelier and seems to handle better than the RT. As I understand it, the newer models are fitting with the DPS II, which is a revised and improved power steering module. I have not ridden a new RT, so I can't say if that changes the handling characteristics on that model or not.
Again, whether it's because of overall improvements or model differences, I can't say; however, what I can say is the newer F3's I've ridden have better braking. Although, I don't like the brake pedal position on the F3. However, I think that can be modified to preference.
As mentioned, the storage on the F3 is very limited. Whoever designed the side cases should be fired. From the outside, they look great, but once inside they're really small and limited. The taillight assembly intrudes into the storage excessively and really limits what goes in there. The top box on the "L" is nice and roomy, but like the side cases, are somewhat light and plasticy, and the hinges on the top box are flimsy and care must be exercised in closing.
Also, touched upon is the frunk space. Because of the change in radiator design, the F3 has a greatly reduced frunk capacity.
If touring, the RT is clearly superior. If daytripping, or if the performance is your issue, the F3 is the better choice. IMHO :thumbup: