conveniently, 538 lists every poll, with a rating according to how well they've done in the past.
let's look at the polls they have listed over the last few months:
Marist (A+): +2, +1
Seltzer (A+): -2
ABC/WaPo (A+): +2
Monmouth (A+): -24, -24, -8, +7
Survey USA (A): +7, +9
Fox/Beacon (A-): -7, -8, +8, +4
Emerson (A-): +4, -2
WSJ/NBC (A/B): -6, +3
Pub Rel (A/B): -6, +4
SSRS (A/B): -13, +2, +7, +7
Quinnipac (B+): -20, +0, -4, -2, +2, -3
Gallup (B): +6, +3, -2
Morning Consult (B/C): -14, -15, -14, -12, -9, -16, -13, -18, -13, -13, +0, +7, +10, +8, +7, +4, +8, +4, +9
YouGov (B-): -1, -4, -1, +2, +8, +4, +4, +9, +8, +4, +9, +7, +6, +7, +6, +3, +5, +3, +8, +6
Ipsos (B-): -1, -1, +2, -4, -8, +4, +7, +6, +1, +6, +6, +4, +3, +4, +5, +7, +2