Hi
Those are subjective questions.
Like some stage magicians, practiced thieves may be able to remove any type of watch band, potentially without the wearer being aware, whether with or without the benefit of distraction techniques or use of brute force.
A couple of users have reported the Sport Band having come unfastened when surfing or swimming in the ocean.
I suggest that you visit an Apple Retail Store or an Apple Authorised Reseller to view and try on different bands in person, in order to get the best idea regarding their relative security and strength.