I voted for Sisko, Odo, and O'Brien. Bashir almost made it for me, but I think those three embody the spirit of the oddball nature of DSN. They aren't Starfleet's elite, or even the Bajoran militia's elite -- they always struck me as a bit of a motely crew -- but like Avis, they tried harder, damn it!
Of necessity, Sisko as the lead is one of the strongest characters. His struggle with his wife's death, then his later conflict between being a good Starfleet officer and reluctant messiah to the Bajorans are what make him unique.
As the ultimate outsider, the initially amnesiac Odo typifies "The Other" character ST is famous for. Humanoid in appearance only, he has a unique perspective on humanoids in general. His shapeshifting ability I always saw as a metaphor for his quest for justice, for order out of chaos.
O'Brien is your quintessential everyman, and the only major non-com character in ST. He's a technological top-kick, the kind of guy you'd have a drink with, and able to get along even with the obnoxious Bashir and the prickly Worf. He's the regular guy of the series.
Red Ranger