'Pin Ups' is really just a selection of covers, and not really representative of his work during that period.
I can heartily recommend Hunky Dory, but then I would say that... it's the Bowie I grew up with, so there will be a certain amount of nostalgia there. I have always owned it in one format or the other. Currently I just have an original early press and a pretty recent vinyl reissue.
Some of the songs you will already be familiar with (Life on Mars, Changes, Oh! You Pretty Things), but it is so much more than that.
I think I gave my CD copy to Macca a couple of years ago, otherwise you could have had that.