Well being a company guy for starters. If you're asking a guy to represent you're company for the length of that persons career, John Cena wins that going away.
John Cena is company first, Ric Flair is Flair first.
John Cena is just as good, if not better on the mic then Ric By Gawd Flair. When Cena isn't doing his kiddy routine, he's hands down better then Flair.
Spare the typical, Flair wrestled and won world titles when it meant something. Yeah whatever. Under Flair's NWA reigns, the WWF title became the world title. Let's not pretend John Cena isn't out there wrestling out there every night. Cena is doing it in a time where he's on live TV every week.
John Cena has a better look, he's more charismatic, he's better on the mic, and he's more marketable. Ric Flair was on Sportscenter, good for Flair. John Cena is selling Razorblades for Gillette and footlong Subs for Subway.