When I first came into the fandom, some of my earliest and most eagerly-written stuff (a lot of which is still sitting on my harddrive to be honest) were Alex scenes. He was easily a favorite character on the show, because he tended to have the funniest lines and the funnest quirks. Like Pooh said, I never really saw him as a "geek," at least in any way that could possibly have a negative connotation. I'd even venture to say that between the two, Alex was actually
more popular than Isabel. Sure, Isabel had the social status, but Alex had friends who... you know... actually "knew what species he was," etc. Aside from Michael and Max—and in
some cases it seems like Max's is entirely out of obligation—Isabel didn't. Alex's only real social faux pas is that he gets [very] awkward when he's nervous. Which is actually kind of charming.
The more fics I was reading, though, the more I came to find that Isabel was comparatively a fairly under-examined character, and as a writer, anything that is under-examined (especially in such a vast spectrum as Rosfic) is very,
very appealing. I feel in some ways that the things I would have liked to say about Alex in fanfic have already been done, and in most cases better than I could have dealt with it myself. I could spout off names of amazing portrayals of Alex—but you already know what they are. Great portrayals of Isabel are available too, of course, but they're harder to find, from my experience, and I did feel as if I had a point of view on Isabel that was somewhat unique and new, at least a look at her from a new angle.
Which is not to say that I ever got tired of writing Alex. I wouldn't even say that I've written any more from Isabel's POV than I have Alex's... just that less of my Alex stuff has made it off my harddrive, again. lol Alex is just too much fun to give up writing. In fact, I have two or three characters in original stories that are somewhat Alex-esque (or at least, they're played by an Alex-aged Colin Hanks in my head.
)
I would probably say that emotion-wise, I'm much more like Isabel... I'm a very introspective person, and am often labeled "shy," just as Isabel is labeled "cold." I've definitely had people who disliked me simply because I was overly-quiet. At school, though, my group was definitely more in the Alex range of people... a little quirky, smarter than your average high schooler and mischievous to boot. Like Alex, we had a knack of "getting away with things" with the teachers, if you know what I mean. (Electrocuting desks? No, we didn't. Clearing entire classrooms of furniture for April Fools, though? Uh, yeah.)
The thing I've always loved about the Alex/Isabel relationship is that in some ways they seem to me to be much more equal a relationship than either of the other two main CC's. With Max and Liz, there's always been the idea that she's "the smallest of small town girls," and then Max heals her and suddenly her life is interesting.... which I've always thought was a little unfair. And with Michael and Maria, it quite often felt like Maria was
teaching Michael how to be... or how she wanted him to be. I'm not saying that that's entirely true (part of it was messy handling by TPTB) but again, that sometimes felt unfair.
Alex and Isabel, though... they didn't really have that. Isabel would have liked to
think she had the upper hand on Alex, but it was usually the other way around. He was always surprising her and meaning more to her than she had intended him to, and their vulnerabilities are so comparable that they just... work. I couldn't possibly say that I love one of them more than the other. That's what's so great about them. I don't feel like I have to pick a side. I'm totally on
their side. If I come to Isabel's defense more often... it's just because I feel like less people do. And that Alex doesn't really need me. Because... he's
Alex. Hee.
and well ... he was the guy in the pairing, I'm a girl ... 
I always wanted to see Alex get a phone call during that time and when Liz and/or Maria demanded he show up for something he would just say 'no' and slam the phone down.