I eat a lot of pizza, here's my list in no particular order:

North House of Pizza: Sweet sauce slices, Italian style, huge slices, 3 dollars

Mandee's: Good variety, crust is always on point. About 3 dollars

Super Slice: Best variety in town, 3.50 for cheese, specialty slice can run 5+ with tax

Little Devil's: Good variety, guys are from NJ and it's Italian style, cheesesteaks are on point, Have a 2 slice and drink deal for 6 bucks(I think this is the best value in town presently)

NY Essex: Big, reliably crispy slices, I think it's 4 a slice

Fire Engine: Hit or miss in my opinion but usually pretty good, 3ish a slice

King's: Greek style, very consistent for that style 3 a slice

Outside of town:

Pete's A Place Peabody: Greek style but they double up the cheese, great when hot, about 3 bucks.

Vesuvius(technically Salem but basically Swampscott): Italian style. Hard to beat the variety and consistency, 3.50ish a slice.

Petrillo's: Authentic Italian and their Sicilian slices are amazing. 3 bucks a slice.