What form do I need 1040 or 1040a with a missouri resident and a non missouri resident spouse?
You use Missouri forms for filing Missouri taxes. 1040 is federal. There are no more 1040A and 1040EZ, they have been eliminated.
Pascal the Gambler
1040 is a federal form, ti doesn't matter at all where you live.
For federal, there is only a 1040 form in 2018. You will have to read each state's instruction booklet to see if it would be easier to file MFS at both federal and state level.
As of the 2018 filing season, ONLY the 1040 still exists. NOTHING about state income taxes EVER affected which form you use to file Federal income taxes.
There is no 1040A in 2018