Depends on what you're used to. I ran a 1.6 TS SW for a year but the economy and performance weren't good enough.
I've owned every engine in the 156 and if you can get by with 27 mpg, run the 2.5 V6. Diesels are good if you do 15,000 + miles pa. The 2.0 is a good compromise and the 1.8 very similar. Personally I had to drive the 1.6 absolutely flat out to get anything approaching acceptable perfomance. That was with a 70,000 miles engine with new plugs,filters, cambelt, MAF, lambda sensors and radiator. Heavy traffic/town use wasn't so bad but I do too much mileage on motorways and fast trunk roads for it to work for me.