I haven't seen the E90f in action, but I have seen several of the 997DF's. I didn't like it at all. It has a very grainy texture to the image, and the colors look washed out and anemic.
If you can, you should take a look at one in a store before you decide. The 997DF is fairly well rated in reviews across the web, but the three that I saw looked like crap. I thought the first one was defective, but after looking at two more since then, it seems that's the way they are supposed to look. But beauty is in the eye of the beholder, as they say. Maybe you'll like it.
I've always liked the way viewsonic's look. Matter of fact, I just bought a P95f+ two days ago, but it has a problem. Sadly it was the last one in the store, and I don't feel like waiting on the backorder.
So I called ViewSonic, and they handled it in a very professional way. They offered to send me a new one immediately, and only when I receive the new one should I send back the old one. I guess they can't do much more than that.
I'm still a ViewSonic fan, however if this second monitor is also defective, that is likely to change...