I have (so far) always booked all my tickets via Delta.com. Wondering if there is any advantage booking via Delta.com vs travel sites. Any pros booking on travel portals without compromising my mileage earning privileges? I assuming I can still manage the flights (e.g. Seat selection) even if booked via the portals. Also, can I still get the Medallion Desk to help etc in times of "trouble" or flight changes?