They look different. Preference is all it is. Some prefer to go topless, others don't. If they weren't popular they would have stopped making them after a year or two...
The Targa top is an expensive maintenance item as with age they leak.
There is more body flex in the Targa, they are noisier on the road.
I love mine with the top on or off. And I really love having the option to make that choice.
