I like djdownload.com best for the following reasons: they're the cheapest, they have no hidden costs (e. g. PayPal fees / VAT etc.), they give you free credit if you're a loyal customer, they have needle-drop previews (they were among the first to introduce it and the preview files have a very good quality) and I had a good experience with their customer service - they were friendly and answered within hours!
Unfortunately djdownload doesn't have the newest releases oftentimes — if you want them, you still have to go to Beatport. Although I really wonder why Beatport is still such a major player. Their flash interface is too slow and it takes ages to load the preview files. And let's just say it's pretty bold of them to sell MP3 files at these prices - especially as a European customer you just feel foolish. I wish, the big labels would 'boycott' Beatport, but of course they also profit from the high margins Beatport takes.