I have never owned an iPad, but I have had an iPhone for four years (albeit not the same device for all four years 😛 ). I always prefer the feel and touch of the screen. When I used to work in the mobile department at Best Buy, I would put on a bunch of Invisibleshields for customers. Installation was always easy. But I really disliked the feel of the screen.
Then they came out with the anti-glare matte Invisibleshields. I thought the texture and feel of that screen was acceptable, but what it did to the image was not.
I've never had a screen protector on my iPhone and I do not plan on getting one. I keep my phone in my pocket and I put nothing else in that pocket, so there's not much to scratch my device with.
I'll look closely into cases though. If the Smart Cover really does have a problem with gathering dirt/crap as you fold it out, then I will reconsider purchasing that. But as for a screen protector? I do not particularly prefer the feel of the clear ones and the image effects of the matte ones. 😛