And to clarify, I'm asking for opinions/advice/etc, since I realized I didn't mention that at all.

GURPS is designed to be an easy-to-pick up system. I'd go for it.

Plus 4e is a pretty different beast from 3e.

For GURPS you would need the basic set and gurps magic unless you enjoy spending a hour creating a whole table of new spells yourself. I also recommend martial arts but that's only because it's a rather fun book and not because anything more is needed. Most accusations of it being slow come from people not knowing the rules from heart so make sure you've got at least combat down to pat so it'll go smoothly. Lot's of optional rules there but start with the basics and bring them to play slowly after the play starts to go smoothly.

Creating enemies and things should be quick. I recommend downloading gurps pdf's and taking a look at what you want beforehand so you know what you'll get.

Since 4ed is a bit different as mentioned and GURPS is very versatile once learned I recommend it.

Of all systems mentioned here, I'm only familiar with 3e (3.5e, to be exact), and I don't quite understand why you intend to dump magic/technology interaction if you decide to settle with D&D.

To me, things like mages breaking clockwork stopwatches or inventors being immune to magic healing were one of the most unique features that made me love that setting. I recommend that you don't get rid of that.

It depends on how much homebrew elements you want to bring into your game, but I personally don't see any insurmountable problems with emulating the magic/technology interaction. Of course, it also hugely depends on how much time you're willing to put into worldcrafting and prep work.

Whichever system you pick up, it would require tweaking. It would suck balls to sort out all the minutae and be left with no party willing to play, so make sure you have one.

4e DnD is going to be hard to work with. I would recommend GURPS of the three you mentioned. Paranoia and 4e just aren't going to work out without a LOT of tweaking.