Changing to 195/55/15 is more rubber, hence in theory will have better comfort and ride but worse handling.

Changing to 195/50/15 on the other hand will actually be less rubber, wheel wells will look emptier but should give better handling. YMMV.

Personally noticed more people change to 195/55/15 rather than 195/50/15 but both are compatible and within the limit of the stock rims which are 6jj et50.