Is this healthy?

I'm really thinking about this question as I make choices throughout the day.  I've been overweight since I was seven.  In that time, I have tried so many things in so many different ways, and I've never really focused on these options as the 'healthy' way to be.  With vegetarianism, I did it because of 'moral reasons'.  I was also 17.   It was part of my rebellion, my mom called me a pastatarian. 
From there I went onto Weight Watchers the first time.  Looking back, each time I've done WW I've bulked up on all the packaged 'snackies' that I could.  I barely lost weight.
Then I decided to do South Beach, which morphed into Atkins.  I lost serious amounts of weight.  I did eat a lot of the right veggies and good meats, but I also bulked up on all the fake sugar products I could get my hands on.  Oh to think of all the chemicals I consumed...  I plateaued a year and a half into it and the plateau became a steady gain.
Which leads me to now.  I know that each of these options *can* be healthy it is just a matter of the choices we make.  That is what I'm doing now. 
I think that is what derailed me this weekend was the mind set of 'getting away with' occasional bad choices because I'm no longer on a strict diet like Atkins.
Instead I need to think about what I eat and decide if it is a healthy choice or not.  This will take some time and training.  I can't lie to or trick my body.  I should stop trying!
How do you assess what are "ok" and "not ok" foods?