It could be that this was my first introduction to Hendrix, but I maintain to this day it is the best of the 'Jimi Hendrix Experience' studio albums. I say this for a great number of reasons.
First of all, lets assume you've never heard an 'Experience' album before, and want to dip your toe in the water. This album is a great place to start, as it eases you in with a nice gentle, yet sublimely funky number, before it crushes your head with Spanish Castle Magic. The album is like a gentle roller coaster ride of funky rocky highs, and gentle mellow dips, with an ease of access missing from the other two studio albums.
So that gets you into it, and opens your mind to the possibility of exploring Hendrix further. At this point you may be drawn to purchasing 'Are You Experienced' and 'Electric Ladyland'. However, you're going to be torn between two extremes; the former is hard, fast and in your face, and the latter segues into many experimental meanderings.
I found myself reeling away from those two, a bit stunned, back to this album, and finding solace in the 'inbetweenness', in which you have both hard paced tracks of the first, and the beginnings of experimentation of the third. That is by no means a bad thing though - in fact, to the contrary you come to the conclusion that while Hendrix can maintain the hard innovative edge, he can also provide enough structure and control to make a tight album that still sounds fresh and original.
Over the years I have also found it is a very layered album. Different stereo systems and even different headphones have revealed nuances I have not been able to detect previously. As a result of this, I have come back to this album again and again. I have owned it on tape, vinyl, CD and now MP3. I wish the same could be said of the other two.
So, in summary, this is both the best album for newcomers, and also, in my opinion, his best album.