Inferior. 'Sub' as a prefix means 'under' or 'below', and indicates that the subject is in a relatively small proportion.
The comma would end up between but and orange.
"You may have an apple or an orange, but you can't have both."
This is because you're coming to a conjunction, which usually has a comma preceding, or coming before, it.
This is the correct way to say it.
Lifeguards must have current CPR, First Aid, and AED certifications.