Hi Badi,
your question may be too general to be answered. Its like you ask: Which is the best dish in the world? My young niece will say Pizza, her brother prefers French Fries and his father a steak. I will take a well-made Dhaal over all of them.
Who is right? Impossible to say. Its the same with tea, you'll have to try some and choose for yourself.
You could start by trying one or two good green teas, Oolongs and black teas. Other tea types are good, too, but the ones I mentioned are often rich in aroma.
And as always, you should not spend too much, but also not too little. You can get 1kg green tea for 5$, but this will be awful tea. There are many good vendors for tea, and some not so good ones

It depends...
Do you live in a big city? Maybe there is a good tea store in your vincinity where you can talk to the people? If not, you can check out the vendor guide of teachat, just pick a shop, and try some things...
Good luck and have fun!