I have never been to New York, but as my profile says, I live in Atlanta, so I've seen the airport and approach quite a few times. The Atlanta airport does not really have any great spotting areas. I would recommend you go to the E terminal to spot planes. The E terminal is the international terminal and there is usually a few non-Delta planes there to look at. Most of the other terminals are full of Delta aircraft and the same thing over and over again is not that interesting unless you really love Delta. The E terminal has mostly Delta too, but there are a few more airlines there to see. The only spotting you can do a lot of is just looking at planes a the gates. There is no viewing deck to observe runways and the views from the terminals are not so great of the runways. There are not lots of really big planes in ATL unfortunately. In the E terminal, where there are the biggest planes, most are still not huge. There are usually a few MD11s, which are big, but mostly 767s. Delta uses lots of those on their international flights. There are very few 747s. You will fly on one to either New York or Atlanta. SAA and Korean Air are the only common 747s in ATL that I can think of. British Airways, Lufthansa, KLM, Air Jamaica, Korean Air, SAA (of course!), Air France, Aeromexico, LAPA, and Swissair fly to ATL, but some of those are not very common. From those airlines you can see A340s, A330s, 777s, A320s, MD80s, 757s, 767s, and 747s. Delta also has 777s, 737s, and 757s in the E terminal. If you plan to go the the domestic terminals, which are T,A,B,C, and D, then there is also spotting. There is lots of Delta in all of those terminals. There is also Airtran, Northwest, Vanguard, American, United, Air Canada (Air Canada flies out of the domestic terminals in ATL sometimes), TWA, US Airways, Metrojet, America West (I think they still fly to ATL), and probably a few other airlines.
From the air on arrival and departure, there are lots of trees to see. Depending on the direction you would fly in from, there is downtown part of the city of Atlanta and that is a very interesting sight. The buildings are really neat to see from the sky. Otherwise that is about all that you would see from the sky. There are roads too, but those are everywhere.
I know that I gave you a lot on Atlanta and nothing on New York, but I hope that helps some and have a great trip!