Wow this thread was made for me. Those cars are basically identical except body work and a few other things.
What kind of transmissions do they have? First thing first, I would go for whichever has a manual. The autos break down a lot. Granted, they are easy to fix, but you should pretty much count on spending around $500 down the road if you get an auto. The 4F27E auto is very weak, especially with upgrades, which I know you don't plan on doing. The MTX-75 is a much more stout transmission and will take up to around 200whp all day.
They both (should) have the same engine, the 16v 2.0 Zetec. It puts out 130 hp 130 ft lbs at the crank. The ZX2 is a little faster because I believe it is a tad lighter, but it is mostly because of the 4.10 final drive.
Now there's a small possibility the Focus will have a 2.3 Duratec PZEV engine. If it does, get on that like white on a ghost. It's rare and the Duratec is far superior to the Zetec. On top of that, you have the new generation motor without the ugly of the 2nd and 3rd gen Focus exterior. You can check easily, the Zetec is black and says 16v Zetec on top. The Duratec is silver and doesn't have a name on it. Also the intake and exhaust sides are swapped around from a Zetec which is more efficient. Intake is in front so it won't get hot.
If you ever want rims, they use the same ones and they are difficult to find compared to, say, a Honda Civic. It uses a 4x108mm bolt pattern and offset has to be between like 42mm-56mm. Not a good wheel selection, but if you look you can get lucky like me and find a relatively cheap set of BBS that look awesome. lol
I can personally vouch for these things which all contribute to how much the Focus kicks @$$!
Trunk space is unbelievable. You can lay the rear seats down and carry as much as a minivan. I carried basically my whole room minus a bed to Auburn and had room to spare. This includes a massive amplifier and a guitar, my gaming PC, router, 360, tons of clothes, massive new comforter, several sheets, 4 pillows, etc.
Handling isn't great but the responsiveness makes it feel that way. I'm not sure if the ZX3 shares the same chassis with the ZX2, but the ZX3 does have a ton of driver feedback which contributes to control. Drive both cars and see which one you like best.
The ZX3 is a dream to work on. I've done several upgrades and have unfortunately had several things break. It comes with the territory when you buy a 10k car. But I do all my maintenance myself, and honestly it's not much more than another average car. I have done transmission work and engine work and it's all pretty easy. Engine bay is a little cramped but if you know the tricks it's pretty much a breeze to get to everything except the oil filter... still a learning experience every time with that one. I've also done brakes. Again, easy. Parts are pretty cheap, and you can get better aftermarket ones cheaper than OEM usually.
That's all I can think of to tell you right now. They will both be fun, just pick the one that speaks to you. If you get the Focus you need to join the forum I'm on. Actually, I just remembered that my favorite thing about the Focus is the community. Hop over to http://www.focusfanatics.com
and give it a browse and you will see what I mean.
Good luck with your car hunt.
Here's an edit with some more info based on what you just posted:
The Focus has a lot of road noise too. It's a cheap econo car and has very little insulation. You can fix that if you really want to with some stuff called Dynamat.
Traction on the Focus sucks with stock tires. You'll want to change them to BF Goodrich G-Force Sports or Nitto Neogens, as those are the best bang-for-the-buck streetable sport tires I know of. You might get like 30K miles out of a set for either of those. Don't think you'll ever need winter tires based on your location, so you can just use summer tires all year.