If my husband was incarcerated from March 2018 thru Dec. 31 2018. Whats best way to file

[Hal_Al]

It depends on more detail.

You can still file as Married Filing Jointly (MFJ) and that is usually best.

Since you lived apart, for the entire 2nd half of the year, you have the option of filing as Head of Household (HoH), if you have a related dependent, that lived with you (usually a child)**.

Your only other option is Married Filing Separately (MFS). You may not file as "Single".

You can use  this tool to do comparison returns:  https://turbotax.intuit.com/tax-tools/calculators/taxcaster/?s=1

**If you parent is your dependent, they do not have to live with you to qualify you for HoH.