modality N2 uncommon casualpolitewritten
ましだ — is preferable
ましだ
A full written guide for ましだ is on the way.
This point is mapped in the grammar Path, but its examples, formation table and usage notes haven't been written yet. The fastest way to learn it now is to meet it in real sentences inside Jengo.
See ましだ in real sentences
Jengo shows ましだ the way you actually meet it: inside real Japanese sentences, so it sticks instead of staying an abstract rule.
Study it in JengoSources Editorial confidence: medium.