I don't agree with the recent posts. Adam was real to himself. Like he said at the end of the show. He could have taken the wussy way out and picked Rachel because he knew that the public and his family preferred her over Samantha.But Samantha was the one that brought out the certain special feeling in him and no I'm not talking about lust. If you ever fell in love with the right person, you knew exactly what he was referring to. That special feeling you get when you're with that one true person who really makes you feel happy. Who when you're with, you smile all the time because there's this halo of love that surrounds you when you're together.
Rachel looked perfect for Adam, but she was missing that one special ingredient that makes a relationship work. It's an indescribable feeling and once you find it in that one person, you never want to let that person go.
So Adam did the right thing despite all the criticisms he knew he was going to face - he was true to himself, to Samantha and to Rachel and in the end that's all that matters.