This really requires a deeper analysis, but I would grab the tempo you get with 1...Kd8. Puts white to the test- do you go after the weak pawn on a5 with 2.Ra7, do you retreat with 2.Re2 to protect the f2 pawn, do you retreat with 2.Re1 to play 3.Rg1, or do you put the rook on g7? My preference here would be 2.Re2- it helps protect the f-pawn, keeps black's knight out of the game for a while, and it also protects b2. Like I wrote, this requires a really deep analysis- so it is more or less a 1 move answer, sorry. Will take another look at it later tonight.