hard sliding uppers look good and sound like a good idea, until you have to go through a drive through, have to swipe your security badge at work parking garage.. . or want to stick your head out a little to check your wheel placements on the rocks. heh.
I'm actually considering swapping out my hard uppers for my strike force zebra doors when they come out with the soft uppers if they have zippered windows.
I had zippered uppers on my last two TJs and loved them.....until I had to roll up to a drive through. Unzippering the windows and fold them back to stick your hand out for the things you mentioned was a PITA to me. That was about the only thing I didn't like about them. Being able to toss them in the back for more open aired feel made me forget real quick though.
I've never had sliding uppers. I think the biggest issue I'd have with them would be to know which way to slide the glass so I'm even with the drive through window. I'd imagine they would be heavier than soft uppers too, but I'll take that trade off if they are more secure than having soft full doors.