Redsn0w or PwnageTool? iClarified says that there's an untethered jailbreak for iPhone4 for iOS 4.3.1 which is the most up-to-date version of iOS as of writing this question.
Let's assume we are talking for unlocked phones. My question is which tool is better - RedSn0w or PwnageTool? My question is valid not only for 4.3.1.

Wikipedia says "redsn0w is a utility to jailbreak iOS devices" and "PwnageTool is an iPhone jailbreaking application for Mac OS X that creates custom iOS firmware images" (cannot post a third link, but that one is easy to find).

Reasoning for the question: I have read on several places that an irreversible thing could be made to a iDevice (iPhone for example) that mutilates it somehow and it cannot receive updates from iTunes with stock iOS and only custom iOSes can be installed. Wikipedia says redsn0w is a jailbreak utility while PwnageTool creates custom iOS.

Second question: does PwnageTool do the irreversible thing I have read about? Does redsn0w do that either?
The only irreversible thing you could do is to upgrade your baseband, eventually making it harder/impossible to unlock. In the past bricking the device was possible, because you were able to reflash the bootloader incorrectly (iPhone 2g) and thus bricking the device.

PwnageTool and Redsn0w are from the same developers team (dev-team) and they are using the same jailbreaking method (as of redsn0w 0.9.6rc9 and PwnageTool 4.3). IMHO both are safe, but PwnageTool gives you more power.