Thats what the forum is here for 
What, so soon 
NFC Data Exchange Format Pretty much NFC Text format
So you can store things like
With an App like
TagWriter
or
NFCTools
Keeping it simple ( I can, or somebody else can expand more if you want it )
M1 is a Mifare S50 chip, that has many names such as Chinese back door, magic mifare…
Pretty much, it has been “cracked” no longer secure, but it is also an older Tech that still has a great presence around the world, used in many hotels and office / apartment blocks, and purely because it is a huge and expensive undertaking to upgrade, and also the average Joe doesn’t know any better, companies choose not to.
M1 can also store NDEF, however and unfortunately it is not as easy as writing to it with your phone
The huge Benefit for OUR purposes, is the abundance of readers still around and the fact it is one of the Few HF chips with a Changeable UID ( Technically an NUID, but that’s the longer story)
The FlexM1gen1a and gen2, also have slight differences…Here’s the link…THAT I SHOULD HAVE JUST LINKED YOU TO INSTEAD OF RABBITING ON 
The DF is the DesFire Chip, Much more secure and capable chip with more features if you have the skills to utilise them, It also has A lot more storage than the M1 ( which has more than the FlexNT) The downside is the UID is not changeable, so whatever you want to use it with ie. for access systems / locks, Transit systems etc you would need the access to enroll it rather than being able to clone a current working card, like you can with other Changable UID chips.
In short pros and cons for both, so start scanning your access/ transit cards etc. one option should come out on top…hopefully
Clear as mud? 