I personally thought the one with the wheel in the back felt more like an upright bike, due to the position of my feet when they moved, they angled downward. The one with the wheel in the front felt different to me. I've read that you should find one with a longer stride because a shorter stride also gives the feeling of an upright bike.
I would really suggest trying them both out. Maybe you can to to a sports store that has a wider range of models to choose from - even if you don't plan to purchase from them - just so you can try the different styles. Make note of the stride length of the ones that feel most comfortable to you.
I regret having ordered mine online without trying it out first, especially since I paid $700 for it
That was in November. In January, I bought a new treadmill and found a good local sporting goods store, and I tried it out. I've not touched the elliptical since, other than to give it a good dusting, lol.