Should they be abbreviated (Ex. TX, FL)? Or should they be fully spelled out?
I have a doubt. What is Ex. TX, FL?
This was a joke but gives you a clear response. Type the full name.
Those two examples you post are easy, but how about MA. Is it MAine, MAssachusets or MAryland... or maybe MichigAn or MinessotA or MontanA.
You could use the two letter abbreviation TX as the value on your database, but not on the list the user is reading.