My choice would absolutely be Mastros. Both Ocean Club and Steak House are terrific. I love the courtyard at Ocean Club over any seat at Steakhouse, but Steakhouse has more choices of non-seafood items like prime rib and veal chop.
If I had to pick another place, I would say the best two steaks I have had other than Mastros was at A Restaurant in Newport Beach. I had a stellar Kansas City and Flat Iron there recently.
Is Turner New Zealand still in business in Costa Mesa? If so, there is no question... Ruth & Morton are crap. I haven't been to Mastro's but Turner's venison filet cooked Rare with carmelized shallots & bleu cheese is on my all time list... and I have had some serious steaks (Luger's is somewhere on the bottom of my Top 10).
You'll find opinions galore on this board, just do a search (see the Search This Board box near the top of the page) for Mastro's, etc.
Personally I'd give it to Mastro's in CM, but I also really like Ruth's Chris. Haven't been to Ocean Club, so I can't say personally. But the "scene" at Ocean Club is supposed to be quite something.
I would recommend Mastro's Steakhouse in Costa Mesa. I have been to both Mastro's and Ruth's Chris and I prefer Mastro's by far.
I haven't been to the Mastro's Ocean Club is there a reason you don't have the Mastro's Steakhouse in Costa Mesa amongst your choices? I have heard the Ocean Club has more emphasis on seafood.