I have used the crosstrainer and even done the interval courses at a good incline. I notice my muscles were staying in pretty good shape, but when I went back to running I had lost some of my lung power. It was harder for me to make it through my miles.
I did keep a good pace on the crosstrainer as well and a good incline, so it wasn't that, there is just nothing that is running..........but running.
just my personal preference. But I will say I did like the cross trainer too it wasn't like I gained any pounds and my musles still looked great.

so both are good.