I like the smoothness and responsiveness of a naked screen. the lightest little tap and my touch is recognized. I have no slippage problems, if you do you're probably pushing too hard or have some really greasy fingers.
unless you wash your hands thoroughly before using the device, your fingers will be smudgingly greasy no matter what. when your hands are entirely clean, there will be quite a bit of friction on the screen because your skin won't have all that grease to glide through. obviously, grease reduces friction tremendously in all things. it's all about good tablet hygiene. I never use my tablet without washing my hands first. there's also another practical reason for it: to keep from scratching your screen. you'll eventually get some pretty hard particles trapped between your fingerprints and sticking to your skin in general.....keep that up and you'll eventually scratch your screen slowly but surely as time goes on it will build up to the point where the scratches become visible. another issue is greasy screens can also allow rough particles to more easily glide between your fingers and the screen, making it really easy to make large swiping scratches. put some WD40 on two of the same knives, and the one with the WD40 will cut into anything much more easily. the oil on your fingers acts the same way.
number 1 tablet rule: clean your dirty hands.