There's no difference between regenerating stamina offline or online (with the resting area bonus).
Those two options, are the only ways to regenerate stamina naturally. Keep in mind that you need to be logged off for 10 minutes before you start to regain any stamina, so if you consider those 10 minutes as a differential you could say online would take less time, but the time it takes to regenerate the stamina is the same.
Also remember that we are considering online stamina regeneration only if you have premium account, got the resting area bonus active and you're at a protection zone.
For every 3 minutes you are logged off your character will gain 1 minute of stamina. However, it will take even longer to regenerate the stamina for the bonus hours since you gain way more experience in them. For every 6 minutes you are logged off you get 1 minute added to the character’s bonus stamina. You need to be logged off for 10 minutes before you start to regain any stamina. To go from 39 hours of stamina to the maximum of 42 hours (bonus) it would take you 18 hours and 10 minutes of being offline.
- Tibia Wiki
There's also a Stamina extension potion, which will refill 1 hour of stamina when drinking it, but this doesn't count as regenerate. Also this stamina has a cooldown of 24 hours.