The best option is probably Andrew Mango's Ataturk. The book has certain advantages. The author is British but born in Istanbul, spoke Turkish very well, had historical training (albeit in a different field) and is reasonably objective. He is not always correct, he did not have access to all (especially archival) documents, but if he is mistaken, it is not because he fails to be objective. To be sure, Mango was certainly an admirer of Atatürk and an advocate of secularism in Turkey, but he does not ignore the opposing views in his account, and I think he does a good job of isolating his private beliefs from his work as a historian.

At any rate, though, I would suggest reading comparatively. The best option always is to read more than one work, compare them, see what sources they employ and how solid their arguments are. It is also a good idea to back reading a biography by also reading a general history of that time and place. Work of Erik-Jan Zürcher can be a good option here. Zürcher is liberal-leaning (in a European sense) and you can feel it in some of his analyses but on the whole he remains quite objective, I believe. I can also suggest Feroz Ahmad's work. Ahmad makes it no secret that he is an admirer of Atatürk but he is rigorous when it comes to compiling historical facts. Though he engages in what looks like outdated class analysis at times (searching for a class base for many things which are probably explained by other things, though often returning to the individuals and their motives in explaining historical phenomena), I find most his analyses to be still valid and objective enough. Surprisingly for some, I can say much the same for Bernard Lewis, who was in fact Ahmad's PhD supervisor. Lewis is the chief orientalist with his debates/arguments with Edward Said. I do not know how good and objective his work on Arab history is so I cannot say anything regarding that. But after all these years, I still fail to see how his work on Turkish history and Kemalist era is orientalist or subjective. Like Ahmad, he is enthusiastic about Kemalism, and again like him, he is often objective enough. This could go on forever, probably, since there are a variety of works on Atatürk and Kemalist era ranging from a work of psychohistory to an 'intellectual biography'. I suppose this gives an idea, though.

My suggestion, in short, is to read Mango's Atatürk and then supplement it with general histories of Turkey, one from Zürcher and one from Ahmad could be quite good.