If he had the choice to kill a million Russians or a million people from Britain it would have been an easy choice. Russians. But it isn't always a black and white choice. Odds are he would have to get a plane to the location because nukes on the tips of rockets would have been very difficult during the war with war technology if things followed a similar timeline. So this likely limits the targets possible to even hit to the western allies minus unless we are talking at the highest point of German power when they were deep inside Russia but truth be told in 1942 a nuclear armed Germany likely wins the war by destroying Russian and the west so it isn't much of a discussion. Unless of course we say they shrunk weapons down enough to put on a rocket. Had rockets able to each Russian cities from Germany, and then also hit the desired target at that range. Then sure it's back to Russia again. But all of that is unlikely. Hitler would target the west less by desire and more because it's all that would be on the realistic target list.