The short answer
Plan G covers nearly everything after the annual Part B deductible. Plan N usually costs less each month, but you pay small copays for some office and emergency room visits.
What Plan N adds in out-of-pocket costs
With Plan N you may pay up to $20 for some office visits and up to $50 for ER visits that don't lead to an inpatient admission. Plan N also doesn't cover Part B excess charges, which some doctors are allowed to bill.
Who usually chooses each plan
People who visit doctors often, or who want the most predictable costs, tend to prefer Plan G. Healthy retirees who rarely see the doctor often save money with Plan N.
Because Medigap benefits are standardized, Plan G from one carrier covers the same things as Plan G from another — only the price and service differ. That's why comparing carriers matters.