For me seeing the animals was the reason to go on this trip - & they did not disappoint! We were lucky enough to go in pupping season - so tiny seal pups were bounding around & playing everywhere - it was wonderful.
I'd suggest definitely going on a live aboard boat (daily excursions are available from a land based hotel but I wouldn't recommend this as the best sightings are on islands only accessible by overnighting on small boats.)
Go for a minimum of 5 days on a small boat (16 passengers max) as anything shorter isn't worth it & a bigger boat leads to less privacy on the islands - animals hate big groups of loud tourists & will inevitably run away!
Go for longer if you can - most ships do 7/8 day trips & this allows you to get to far reaching islands & away from the less adventurous 'cruisers' in big boats.
Quick Tips:
If your a diver take your own gear or arrange rentals in advance. Remember to bring CASH only to pay your National Park fee at the airport - they're not joking when they say they only take CASH!!!
Take camera film & batteries - lots of them - once you're on the boat there's nowhere to stop & buy it & shops at the tiny airport are often closed when the planes arrive! (Same goes for sun tan lotion & medicine).
Take snacks - the food on the boats is good but repetitive.
Take a water bottle.
Take sea sickness tablets!
Best Way To Get Around:
Sailing on a small boat.