I agree, just order the format appropriate for your machine. Sometimes, when you get designs, rather than ask you which format, the vendor will send you all the formats. I generally delete the ones I can't use.
If you order from a vendor who keeps your history on file on site, if you change to a new machine that takes a different format, you can go into your history and change the format on the designs you have already purchased and download them in the correct format for your new machine.
If you come across a design on a vendor's site that is not available in your format, they can generally reformat it for you to be compatible with your machine.
I have a Brother and ordered a design the vendor had available but not in my format and they were unable to reformat it. I sent the design to Brother and they reformatted it for me so I could use it.