rogue 12/fighter 8.
you get 7 feats and 6d6 sneak attack, 2 attacks, no fail skills,
feats: alert, sharpshooter, skulker, observant, lucky, and +4 dex
You might want to discuss with your DM what Skulker would actually grant you in terms of benefits post stealth errata. Now that you only need to be "unclearly seen" instead of unseen to hide, it's possible that the chief benefit of Skulker is now redundant since being lightly obscured / having half cover is by definition what being unclearly seen means. You could save yourself a feat or could come up with an alternate benefit together.