The Dyna line rides better due to the rear suspension frame geometery,the softail are intended to replicate the rigid or hard tail bikes of days gone. The FXR line was HD`s best handleling bike which isnt made anymore. It had the swingarm mounted rigid in the frame not the rear of the engine case like the later FXD series and subject to motor mount flex and wander,which can be cured a few ways if you wanna spend the bucks. As mentioned dont be afraid of a EVO bike,better mileage,no cam issues,mass aftermarket etc.
Go rent one of each and feel the difference,its cheaper than buyin a bike you end up not liking. Looks go so far then you`ll realize your screwed,not sayin the softail line is bad,just different. I have no problem riding my my 93 springer softail 500 in a day,if I was in need of speed and more miles the FXDXT does it. I sold my bagger,great for long distance in crappy weather,not much fun in the twisties.