I lean toward the ironic reading. Austen's characters speak sarcastically at times, and I don't doubt that she herself enjoyed using her wit that way in person. But applied to social commentary, I would be more inclined to call it satire.

Austen, like Thackeray, reminds the modern reader that satire can be delicately done and need not ridicule its characters. Still, characters like Mr. Darcy and Mrs. Bennett--or Emma, in my personal favorite of Austen's novels--are deliberately overdrawn to reveal the foibles that accompany their station in society. Would you not call that satire?