I am definatly saying Low. You just can't beat it. It takes a few listens to get used to the shear avuant-guarde-ness (is that a word?) of it but when you do, it is amazing. The other Berlin trilogy records are good as well (especially "Heroes") and the other recomended are:- Diamond Dogs Station to Station Scary Monsters "Heroes" David Live
If you to like Low, I recommend Krautrock music, as that was the influence. Try Tangerine Dream for the instrumentals on the B-Side and Harmonia for the vocal tracks on the A-Side.
You must be too young I.P. Hunky Dory was Bowies pinnacle, The Man who Sold the World highly underrated, Ziggy Stardust and Alladin Sane were brilliant. Young Americans onwards is mainly tosh. So there!
You're getting closer. However it's wrong to say the stuff after 1974 is tosh but it simply isn't as great as the superb albums M Sparks mentions. The sidebar advertises the album called the Best of Bowie 69-74. In my view you could just have called it the best of Bowie full stop because that was when he did nearly all his best work.
However I don't think there is any debate about what the absolute best Bowie album is. Ziggy Stardust is an album which should be on everybody's desert island list. You are of course entitled to disagree, but you would be wrong.