Hi. it is kind of a hobby of mine to explore aquariums around the world. It's always pointless to look for the "best" anything because it all depends on what each individual wants that day. Here are five not mentioned that I really enjoy:
Marine World Umino Nakamichi (***uoka, JP)
OK. I am biased... ***uoka is my favorite city in asia. Its clean, beautiful, and just... I don't know.. PERFECT. The aquarium is great because its on an island off shore, so you have to take a ferry through the beautiful ocean waters to get to it in the first place. There are a lot of good fish to see... Especially sharks. I guess the biggest attraction is that its one of only 3 places in the world where you can see a MEGAMOUTH SHARK! Its preserved dead body of course... And it is a juvenile. But still... fascinating.
Underwater World (Singapore)
This place is HUGE. And has a ton of shark exhibits. You can even eat in a rotating diner that moves through a shark tunnel.
New England Aquarium (Boston, USA)
This place has a great variaty in an easily accessible layout. Fair prices, and a great seadragon exhibit. The giant ocean aquarium tube that you walk around is sort of common place now in aquariums, but this one is still well thought out and enjoyable as any. Theres a pretty big freshwater section with a lot of big monster cats and piranha and such. Another great thing here is that you can purchase tickets to go whale watching and the boat leaves from right near there out to the ocean.
Oceanworld Manly (Sydney, Australia)
I think this one has the largest collection of marine life anywhere. Its famous for letting the customers swim with the sharks.
National Aquarium (Baltimore, US)
This place has a ton of animals and is really big. I just hate that when I went, it was crawling with people and I didnt have a good time... I want to try again during the week.
aquariums like that, thats HUGE