GURPS, both answers.
Hard as it is to believe looking back, GURPS was the second RPG I ever bought and read, right after the Mentzer D&D Basic/Expert sets. Talk about moving up to a totally different league!
It's not like GURPS (particularly in its 3rd Edition Basic Set incarnation) was terribly complex, but I found myself dealing with a much bigger page count and, more importantly, a much more wide-open approach to campaign and character design. To go from "seven classes (including three race-as-class options) go adventuring in dungeons for three levels and then maybe start doing wilderness adventures" to "pretty much anyone, any time, anywhere" - well, it was a real trip, let me say.
I was completely transported by the options that GURPS opened up. I literally had no idea what to do, paralyzed with the many options. My brain clearly short-circuiting, I think the very first character I made was an epileptic gas station clerk. Just to prove that such a thing was possible, I guess? I min-maxed the hell out of him, regardless.
Eventually I settled down and started building (not rolling!) characters that had some sort of thematic consistency, who weren't necessarily min-maxed to the gills. To this day, GURPS remains my favorite system for character creation. But it's in that versatility that also lies the rub.
As GURPS grew increasingly...not complex, but detailed, I guess? As it grew in girth, the mechanical options certainly opened up more and more. Fourth Edition actually did a great job synthesizing the previous 15 years of growth, but somewhere along the line GURPS character creation stopped being as much fun as it used to be. The addition of so many new Advantages, Disadvantags, and Skills, along with Modifiers and Techniques, rounded out the system and allowed for unprecedented customization, but it also made the process of character creation much more detailed and time-consuming. Nowadays, it's really a good idea, especially if you're building a character from the ground-up and not using any Templates, to have a computer do a lot of the heavy lifting for you.
And although GURPS Character Assistant is a great program and an awesome tool, somehow it's just not as much fun as sitting down with a simple one-volume Basic Set, a character sheet, and a pencil, and min-maxing that epileptic gas station attendant.