Least desirable maxillary major connector is:
U' shaped (or) Horse shoe shaped major connector:

Least desirable palatal major connector.
Poorest designed palatal major connector, because it lacks rigidity.
This is indicated only in cases of inoperable tori, extending to the posterior limit of the hard palate.
It lacks rigidity.
This design leads to increased ﬂexibility and movement at the open ends.
The wider the coverage, the more it resemble a complete palate (palatal plate).
Complete palate
Double palatal bar
Horse-shoe shaped
Closed horse-shoe