What is the most interesting and best attraction in Dubai?

It depends what attracts/interests you and where you are from/what you are used to. A souq for example can be attracting to a person who's not used to have them in his/her own country but not attracting people coming from countries having souqs/bazars also.

Most people also are eager to visit Burj Al Arab the so called first 7 star hotel.

Taking into consideration that Burj Khalifa is the highest tower worldwide so far you may find visiting the same as the most interesting attraction in Dubai.

Another attraction is the Wild Wadi Waterpark, Ski Dubai in the Mall of the Emirates, the Aquarium in the Dubai Mall, Dubai Creek, Dubai Museum, etc.

In case you can't make up your mind, just take a Big Bus Tour which takes you to all tourist attractions.

There are many attractions in Dubai and it all varies what attracts you most. If you had plans to sail

On yachts along the Dubai coast on blue water through sky touching buildings, then you will find

It the most attracted thing over there. But don’t forget other attractions like dinning on dhow, fishing in deep sea water and desert safari.

You will be able to see all attractions in 3 days. How about seeing all of 'em?

To me, a walk around Dubai Marina in the late evening is interesting.

or do as H has laid out.

the burj khalifa , the tallest building in the world is the best