Hi Tao-
I agree pretty much with Jim and Doug. We recently completed a 9700 mile trip, with about 6600 miles of it over five weeks towing the 19. We tow with a 2000 Toyota 4 Runner and use a WDH. This trip had pretty much all you would encounter in roadway variety except for off road/back country towing. The 19 was superb following along, with nary a twitch as the big rigs went by and even in quite windy conditions it followed with out a tremor. We tried to tow at about 60-65 mph for economic/mechanical reasons so as not to stress tow or driver and it worked seamlessly. Once or twice I did find us in excess of 75 mph and Houdini was just following meekly along. The 19 appears to me to tow more calmly/ smoothly with less bounce. ( We used a WDH with the Casitas too, so a sort of apples to apples in that aspect...)
Long hills and mountain passes slowed us down considerably and in some cases on the really steep passes we were down to about 40 - 45 mph. (Hey, we owned a VW camper van at one time - )you just stay to the right and let the rest go by. I did not really notice much of a difference between our 19 and our previous 17' Casitas in climbing hills. As for maneuvering, I found the tandem axle easier (or so it seemed to me) - a much more forgiving trailer to back and turn. We were able to get into some pretty interesting places without a problem.
To sum up, I don't think there is a dramatic difference but I feel that the 19 is calmer in towing and more forgiving in maneuvering. The biggest difference is the larger interior space and bed, and to us it is most emphatically worth every penny! Hope this helps in your decision. Ian