I have leather seats in both my (fully enclosed, not Fiat) daily drivers. But for my new Spider, I chose the Classica in large part because I preferred the cloth seats for the way I'll use the car. I'm very pleased with that choice.
Pretty rugged fabric that keeps you well planted in the seat, and the overall construction and stitching looks solid. Haven't sat in the Lusso, but against the Abarth, the Classica seats initially felt more cramped. They are well-bolstered and I have fairly wide shoulders, so I feel constant pressure on the outside of my shoulder blades, pushing my shoulders forward. However, after a few hours, I realized it's actually a pretty comfortable posture.
I've had convertibles in the past with both leather and cloth. I prefer cloth due to the fact when driving on a hot day with the top down you don't get as sweaty so you are more comfortable. That's one of the reasons I got the classica. Also, this is my summer car so would never use the heated seats.