Gold and Diamond Park is a good place - if you are well prepared. What are you looking for? I have plenty of advice to share on round diamonds in the 0.50-2ct range if you are interested :)
the best place (and even a little haggle) in meena bazaar in Bur Dubai. I found that they have a great selection and also the prices are reasonable compared to what I have seen in the malls and in the souks.
good luck.
Tejouri in the gold and diamond park - couldn't ask for better service and excellent prices. Always research current prices before you go - which ever one you choose.