Short flippant answer? Whichever one works for you!
Slightly longer less flippant answer: I count calories, that works for me. But everyone is different.
Why don't you try just changing a few things first? One suggestion that is often made is to not try and change your eating habits initially, just write down everything you eat and do in a normal day for a couple of weeks. Then have a look at what you are eating, and when (emotional eating is a big trigger for some) and see what you can change.
I'm a little concerned at your aim to lose 70lb by September. The idea of putting a time limit on a goal may be great for other things, but it doesn't tend to work for weight loss. Life happens. Things crop up which may cause you to lose weight slower than you plan. Doesn't mean you have failed, just that your goal maybe wasn't realistic in the first place.
What you have to remember is that no matter what plan you choose, this isn't a short term fix. You can't "go on a diet" and then go back to how you were once you lose the weight. This is a long-term, forever lifestyle change.
I usually hardly do exercise, but I have a treadmill in my house that I will start to use once I find the right diet program.
Why not do it the other way round? Why not start walking on the treadmill while you have a think about how you can change your eating plan into one that will help you lose weight and get healthy for the rest of your life? Don't wait to get on the treadmill. DO IT TODAY! (Yep, that was my frustrated side coming out). 5 minutes, 10 minutes, whatever you have the time for, it will be more than what you are doing now. And your body will thank you for it.
Good luck, and keep checking back in. The chicks here are very supportive and encouraging, but won't hesitate to kick your butt if they think you are slacking off or making excuses!