With the Gnex, there's very little downside. When you unlock the bootloader, you will wipe the phone completely, but this is generally true when unlocking a bootloader for the first time. If you make backups and follow the basic guidelines of flashing a ROM, you won't have any issues with stability on any of the major ROMS. AOKP on a main release milestone build, rasbeanjelly, mmuzzy, CM10, and the recent stable build of LiquidSmooth are all options that will not require fiddling to provide a stable experience. If there are particular apps with known issues on an unlocked device, it might be worth looking to see if any of these options have found a work-around.