TMZ Sports Show: Katherine Webb and AJ McCarron -- Engagement Ring Wars

AJ McCarron and Katherine Webb finally got engaged -- but so did Matt Stafford ... so, sorry chicks ... but we gotta do it: WHO'S RINGER IS BIGGER??

Plus, Floyd Mayweather Jr. shows off his own massive hunk of bling -- 60 carats blanketing a watch!! Typical Mayweather waste of money ... or beautiful collector's item??