"Swimming is good."
The word جَيِّد = good in any case.
The word طَيِّب is used to say kind/charming/nice/enjoyable. It can be used to describe people, and then means kind. It can also be used to describe things that one experience (food, music, hobbies...). If you say for instance اَلْسِّباحة طَيِّبة, that would mean "Swimming is nice/enjoyable"