The Audi A4 is a compact executive car that has been in production since 1994. The fifth generation of the A4, introduced in 2015, is available as a sedan or wagon. The Audi A5 is a two-door coupé that has been in production since 2007. The second generation of the A5, introduced in 2016, is available as a coupé or convertible.
There is not a definitive answer as both Audi A4 and Audi A5 are great cars. Some people may prefer the A4 because it is smaller and more agile, while others may prefer the A5 because it is larger and has a bit more power. Ultimately, it comes down to personal preference.