What is the difference between QuickPE and password reset disk?
In a nutshell.
A windows (Vista/7/8/10) install DVD boots to a (minimal) PE (Pre-install Environment).
From it you can manually perform a number of steps that allow you to reset a password.
QuickPE is one (among a few) "builder" that allows to create (still starting from an install DVD/.iso) a slightly more "complete" PE, allowing in the process to add additional tools/programs (such as the recommended NTPWedit) that can provide the same ultimate functionality (resetting a password) in an "easier" way.
The tradeoff is between the (minimal) complication of building a new PE and later having an easier password reset vs. using what you already have (the install DVD/.iso) and have a (slightly) more complex set of steps to perform the password reset.
For a one time only use (and provided you already have an install DVD or can easily "burn" one from a .iso) I would go for the second, if you plan to create something that may come of use also in the future, the first is more advised (as it will constitute a "more featured" recovery environment suitable for solving possible future issues of different nature).
The other proposed option of PassPass (if applicable) is slightly different as - it doesn't actually "reset" the password, but rather it "by-passes" it.