First, and I say this not to be nasty, but you are not "creating the Media Creation Tool" you are using the Media Creation Tool to create install media. That is it's purpose for being, to allow either the machine in question to be upgraded (if you choose the Upgrade this PC option it will not even create separate media, but will do the good, old-fashioned upgrade process launched via the website) or to create installation media that you can carry from machine to machine to upgrade them.
You can create media for either a 32-bit or 64-bit machine on either a 32-bit or 64-bit machine. What's pivotal is the contents of the .iso itself, not the platform on which it is downloaded and then converted into bootable media (DVD, USB, or both).
What you do have to be careful of, if you are using the Media Creation Tool to create that bootable upgrade media, is that you use the correct version for the machine you are trying to upgrade. You must not only have the correct "bit match" but also the correct Windows 10 version match (Home or Pro) depending on what version of Windows 7 or Windows 8 is on the machine being upgraded. You cannot do a free upgrade, for instance, on a Windows 7 Home Premium machine to Windows 10 Pro. You must upgrade (if you want a free upgrade) from Windows 7 Home Premium to Windows 10 Home. I would imagine that Windows 7 or Windows 8 in their Pro/Ultimate versions might accept a "downgrade upgrade" where you'd go to Windows 10 Home, but you really wouldn't want to do that, so carrying along the correct upgrade medium for the machine in question is critical.
You can definitely upgrade your own PC using installation media made from the ISO file from the media creation tool. The only real disadvantage of doing this occurs over time. The online "Upgrade this PC" process uses the latest (or next to latest, sometimes there's a lag) build of Windows 10 when applying the upgrade. The installation media you burn from ISO is "frozen in time" and will use whatever build you happened to download when you downloaded it. As time goes by this build becomes more and more "stale" and then the resulting upgraded system will have a lot more Windows Updates that must be applied to bring it up to the current build. This issue can be avoided, to some extent, if you keep an eye on when "the big dot releases" or a change in build number occurs and then you download new copies of the ISOs via the Media Creation Tool and burn new installation media from those.
As to the USB and DVD options, I myself lean toward DVD, but that's because all of the systems I've upgraded have optical drives. What's going to drive the USB choice, though you can use that on machines that have optical drives, is when you encounter a laptop that never came with an optical drive in the first place. The basic technique of updating UEFI/BIOS to change the boot order to look at the desired boot device first, whichever it is, is essentially the same. Then you change that boot order back after the upgrade is complete.
Edited by britechguy, 04 January 2016 - 10:23 AM.