Of all the civs, I'd say that there is no friendliest. I usually play as a warmonger. Later on when I've got communications with everyone, they're all annoyed and are likely to demand tribute (my refusal causing them to trigger a world war). If I play as a builder, I nearly always get sneak attacked, regardless of whether it is a low aggression civ like France or India; a mid-level aggression civ like America or Greece; or a high aggression civ like Zululand or Germany.
If I'm going too well, they'll always be hating me, unless I've signed them into a military alliance or traded luxuries to them. If they are going poorly when compared to me, they will sometimes gamble on a seemingly suicidal sneak attack. If they are going too well compared to me, they'll get very demanding.
I don't believe a single civ to be more hateable than any other, regardless of aggression level. Its mostly their situation that drives them to do things that make me hate them for the rest of the game. I've even had situations where Bismarck and Shaka are my most loyal allies regardless of the fact that they are the most aggressive civs in the game, and France being conniving scumbags despite their apparent passive attitude.