GURPS is my favorite. When I would GM, that was my system. Yes, it is "dicey." However, it is cross-genre. It is easy to move characters across time, space, and dimensions. And when you switch from say "cowboys and indians" to "trans-universe cyborg goblin hordes from the Lower Planes," everyone is familiar with character creation and combat rules.

GURPS has more "real-world" application. Spending a half-point on a skill translates into basic familiarity. As an example, I am familiar with constellations. I am no astronomer. However, my basic knowledge of stars and their alignment helps me find my bearings and how late it is in a season. If my character doesn't have that skill, I can't apply that knowledge to set a course or predict inclement weather. To me, that's role-playing.

Same with Champions. The system is also heavy on cubes, but ultimately it provides for a solid base and consistent play. Though I have found Champions / HERO System works best for superhero campaigns and really does not translate well for other genres.

Marvel Superheroes is fun if you're not serious about a campaign. Good old Dungeons and Dragons is great for strictly D&D. RIFTS is good for combat-oriented campaigns. An oldie but goodie that is D20 is Gamma World. The Elfquest RPG is largely percentile-based. If you want to modify or create your own system, Elfquest might be a good platform.