BlackRa1n is said to be the easiest and quickest jailbreak solution so far. But here’s the most important difference between BlackRa1n and PwnageTool:
BlackRa1n requires you to update your iDevice to OS 3.1.2 and then jailbreak it. Which means your Baseband will be updated and would not be able to unlock your iPhone later. PwnageTool, on the other hand, creates a custom firmware which preserves your Baseband from updating so that you may unlock your iPhone later if you want to.
Here’s a guide: how to jailbreak iPhone OS 3.1.2 using PwnageTool
Download BlackRa1n Jailbreak for Mac: