I should put these carbocations in decreasing order of stability.
Structure 1 is a primary carbocation.
Structure 2 is a secondary carbocation.
Structure 3 is a tertiary carbocation.
Structure 4 (a primary carbocation) and structure 5 (a primary carbocation) are less substituted, but one could form resonance structures.
Therefore I would say 5 > 4 > 3 > 2 > 1.
But I'm not sure why 5 should be more stable than 4. In both cases the positive charge is stabilized by the + I-effect through the sigma bond of the two methyl groups and both can be stabilized through the free electron pair of the heteroatoms.