I think SrI Lanka
The costal tourist destination in Sri Lanka is seasonal. In May to October in West Coast Sea is rough. But at that time East Cost Sea is cram. During the other days west coast is cram and east coast is sea is rough. So you can select your destination as such. But Central Island where well known “CEYLON TEA” is grown there is no seasonal deference. In August there is huge cultural procession in central part of the country. Well dresses elephant is common. It is a very nice and colorful religious event. In hill country of Sri Lanka you can see lots of beautiful seiners. Traveling to upcountry by train is more enjoyable. Unawatuna, Hikkaduwa, Trincomalee are the best beach of Sri Lanka You can start you Sri Lanka inbound tour from beach town Negombo which is close to International airport and also end there.
I don't think people should make plans that far ahead. They never last. Your first priority is to save money and by the sounds of it finish school. Deciding where to go is the least of your problems. All places have its pros and cons but I don't think any of those places are bad.
China is beautiful, but the people can be quite douchey at times. Greece is also very nice, the culture is quite cool but it's hard to experience it because it's quite westernized in most pasts of the country. Iceland is stunning, just very expensive. No one goes to Iceland to just chill in Reykjavik. They do $hit all day, every day and everything you do is expensive. So pros and cons where ever you go.
It's good to hear that you are preparing for your next tour. I think China will be a good choice for you. Beijing, the capital of China,definitely worth a visit. I traveled there twice, and really enjoyed the great wall, the forbidden city. they are really magnificent. for more info, i 'd like to recommend you the following link, very useful. you can find more about China.
New Mexico is really more interesting I think. The southern and northern parts of the state are very different. Try looking up the Taos Pueblo near Taos, NM.
You are welcome to come Nepal and see Himalayas. Experience difference, visit spiritual buddhist and hindu places.