Getting the code for free from the original carrier is always the best option. It's free.
If you have to go to a paid provider of unlock codes, most of the members on this forum will recommend Horizon Wireless
They are a reputable outfit and a forum sponsor. Almost everyone who uses some online discount unlock outfit ends up getting scammed, or gets a bogus code, and has to fight for a refund or a new code. And when that nightmare is done, you're still at square one with a locked BlackBerry. None of that nonsense happens with Horizon.