Stacey,
I first heard about the Core plan this week in my WW meeting. For me, I'm not interested... only because I very much need to use portion control with my food to keep on track. Overeating (actually binge eating) made me overweight so I am wary of a plan that doesn't have a member count Points, unless eating non-Core foods. Too risky for me, personally speaking.
Which is easier, well, that's hard to say. It depends on why you have not succeeded at losing yet... I would suggest you give both a try and see which you like better. WW is stressing that if tried out, each plan be followed for a week at least to see how your mind and body handle the changes
I think Flex is great. I used it 1999-2001 to lose 50 pounds.
As way of explanation as to why I am over 200 pounds now: WW did not fail me, I failed myself because I gave up following WW... and went back to binge eating thinking it would make me "feel better" when I was in the middle of a very stressful relationship. Big, big mistake! It didn't... but I had to learn that the long and hard way
Good luck! I'd be interested to hear how WW works for you too!