Much debate on this point. Try two sites to help you make your choice:

www.modchip.com
www.playstationmods.com

Purchasers of each will say theirs was the best choice. So far as I can see, it's as broad as it's long. I use modchip.com's solution on a Jap PS2. When you've decided, get the modchip installed by a competent electronics expert who is used to small soldering tips.