They sometimes have a 737-900 on that same route, I think. Probably depends on traffic; day of the week, time of year, that sort of thing. And doubtless also availability. But it's always something bigger from here to Atlanta. Never an RJ, so far as I can recall. Don't think I've even seen an MD on that particular flight (DL2084), though I did once on another (I think later) flight to ATL: DL2461. I want to say 2461 was sevenish. They no longer have a flight that late in the evening and the number is assigned to a SEA-PDX flight now. (Not that there's any shortage of flights to Atlanta even without that.)