My choice is the third part, and only the third. No matter how many times I play it, I never get tired of it. Excellent design, a wonderful world, and the ability to create maps, which is very important.
I didn't like the fourth part at all; in my opinion, it's the worst part of the series. Almost everything is terrible. I have nothing more to say, and there's nothing good to note.
The fifth part of the series is very good, but not what I expected. I got tired of it very quickly. It's beautiful and diverse, but it's repetitive. And I prefer older games to newer ones. New games don't excite me.
Therefore, the third part, and again, the third.