"Ender's Game" (the first story) is an absolute must read and in my opinion is the best of the lot. I read them in the order that they were published rather than in the chronological order (i.e. when the stories took place within the fictional time line). With each subsequent book I enjoyed the series a bit less, and for me the series bottomed out with Xenocide. I felt that it then began to pick up again with later books and I was happy that I finished the entire collection.

I am not trying to discourage you from reading the series, as Card is a fantastic writer and the collection of Enderverse books are all pretty good. If you find that you are liking it and then Xenocide disappoints you, it does get better again after that. In my opinion, though, none of them quite match "Ender's Game", though some of the others do come close.

If you take on the series, you might like to glance at this diagram:
http://upload.wikimedia.org/wikipedia/en/9/91/Enderverse.png

The events in the collection of Ender related stories do not happen in the order that the books and short stories are published in. I think most people read them in the order that they were written and this is likely the best approach. However, if you find that you are more or less interested in certain plot lines, the above diagram may help you find what you want.

Ender's Game! It's considered one of the best sci-books ever written.

I must agree with anyone else here, The Game of Ender is the best by far

go to a library and read them all.....find out for yourself and dont scab off other ppls knowledge