We'll need some more information to help you:

-- Which other programs are you already a member of?
-- What class/booking code are your CX flights?
-- Where else do you normally travel, and on which carrier(s)?

I find the CX program is quite good if you're flying CX a lot and particularly if you fly enough to earn status. In this scenario, the relatively generous service benefits of MPO (lounge access even for low-tier elites, seat guarantee for mid-tier, etc) start to balance out the poor earn/burn ratio. It can also often be the only game in town if you're flying CX periodically on discount Y fares (OW in general doesn't do much for discount Y flyers outside their "home" carrier, with a few exceptions).

But if this is the only CX trip you're ever likely to take, it might be worth sticking with a OW program for a carrier you're likely to fly more often, or where you can get a co-branded credit card in your area (if that's your thing). For example, BA charges high surcharges on award tickets, but also offers significant tier bonuses if you're going to reach an elite level.