For me, the best single attribute:
- Scientific: Cheap buildings that give more culture than the religious buildings and boost research. 3 Free techs is a little bonus. Also start with Bronze Working for early spearmen and 1 tech from Iron & swordsmen!
Still good:
- Industrious: Double-speed workers mean that I have half as many doing the same job (smaller payroll). Also, during the beginning of the game, when I have just 1 or 2, double-speed is huge for improving cities & claiming iron quickly. Also can save you from bad terrain. Extra shield for a Metropolis is pretty much nothing though.
- Militaristic: Cheap barracks means that more towns in the Ancient age will have one. Also, you get way more promotions. I hate fighting Militaristic civs & being non-Mil -> when your units lose, the defender gets promoted so your attack netted nothing! Also, more chances at Leaders.
- Religious: After several games, I've gotten used to playing without switching govts too often. Cheap temples are nice, but I rarely need cathedrals so quickly. Keeping people happy is a score thing, so I find this trait a little less than the best.
- Expansionist: If the great start was guaranteed every game, I might put this one at the top.
I don't care for:
- Commercial: All the studies I've seen have shown little improvement in corruption. 1 extra gold for a Metropolis. I'll pass. Start with Alphabet which is valuable to trade & helps get down the tree but doesn't give you any buildings, units, or wonders to start with.