I love Ranked Arena.
IMHO it's the best balanced best matched competitive FPS I've ever played. That's not saying I'm any good at it (gold scrub here for life), but I feel that it is nearly always well matched. Although there is the occasional extremely annoying diamond that slips in or somehow the occasional all plats vs all golds. Friends joined with higher level friends I guess? There's also a steady grind that unlocks interesting items - keeps me occupied.