Have you test ridden each bike? Try to take each one out for a nice ride -- not just around the parking lot. You need to experience the difference in how they feel and their efficiencies to see what's important to you.
I was in a similar situation about a year ago. Started out interested in getting some exercise so I purchased a comfort bike similar to the Navigator. It felt so comfortable and cushy at first compared the hybrid. Nice big seat and fat tires that absorbed all the bumps. However, as I started increasing the length of my rides I found the comfort bike to be not so comfortable and it started feeling very heavy and slow. I wanted to ride longer and faster but it just wasn't enjoyable on anything over 5 - 10 miles. So, a few months later I got rid of the comfort bike and bought a hybrid. And what a huge difference! Much more comfortable, faster, and enjoyable. It's been almost a year since then and now I'm thinking about getting a road bike, but that's another story :-)