Do you mean what do I want out of a system? Or more than that?
I mean, specifically, what do you envision your game sessions looking like?
Are the PCs a band of adventurers scouring dungeons for loot and fighting forgotten horrors in the process? Or, are they individuals with complicated goals and beliefs, defending themselves against moral situations?
How do you envision the typical session? Is there lots of fighting? Lots of interaction and banter between the PCs and NPCs? Does everyone work together? Or, is there in-fighting and intrigue, betrayal and allegiances formed and broken?
What's the world like? Is it magical and fantastical? Is it cold and unforgiving? Are there slavers? Or, friendly wizards in towers?
I mean, when you imagine your perfect session, what does the game look like?
I think you need to figure that out before you decide on a system.