After years of only using DragonDoor cast iron bells, plus a pair of Rogue cast iron 20s, last spring I got pairs of 28 and 32kg Kettlebells USA Paradigm Pro Elite competition style bells (I already have cast iron bells in these weights so I have been able to compare them directly).
I must say that I now prefer the competition bells for many purposes.
The 35mm handles (a lot of older styles of comp bells have thinner 33mm handles) are slightly thinner than the cast iron bells, and to me they are "right sized." The handles are very round and even and the surface has a nice subtle bare metal grain texture (more so than other comp bells that have more polished handles) that works well with or without chalk. The bells sit very nicely and comfortably on the forearm and in the rack. The space between the horns is actually wider than on the cast iron bells and more comfortable for 2-hand swings. Even though the bells are physically larger than cast iron 32s, they seem not to clank together when doing exercises with doubles, whereas the cast iron bells do (the widest point of the cast iron 28s is the outside of the handles, whereas the widest point of the comp bells is lower, at the circumference of the bell).
The straight horns on the competition bells are less comfortable for gripping in goblet position.
Since the competition bells are a little taller, they seem a little slower and less responsive when catching cleans and snatches, but I could easily describe this characteristic as "smoother" as well. Edit: To clarify, the more your technique rotates the bells directly over the top, the quicker and more responsive the shorter cast iron bells will feel. The more you keep the bell below your hand, the smoother and better balanced the competition bells will feel.
I have not tried the comp bells for bottom up work, but I would expect the cast iron bells would work better there because of the lesser overall height.