The addition of the SRAM to the ordinary Comfort doesn't surprise me John. Giant were forced into the dearer SRAM since Shimano Nexus hubs were being changed and the 4 speed disappearing, not before time as it had a pathetic 184% range. Obviously the 252% SRAM range is far superior, and the only minus with it is that it's gear change is slow. Despite that, it's been voted the best all round hub gear in the world at various times and it's extremely tough. There's even a Cargo version with a 225% range that can withstand daily commercial load carrying.
As for the best, it's as said above. I prefer the Twist for it's lightness and ordinary bike qualities, and I don't like suspension forks, but in a hilly area there's the cost of adding the P5 for the best gears, around £200 extra in all. The standard 3 speed is fine in a moderately hilly area though.
The Comfort with the Nexus 4 hub adds just that, comfort, due to the suspension forks, plus the non wearing convenience of the hub brakes. I don't think the hub dynamo a particular improvement on the separate dynamo of the Twist. With the SRAM gears it's improved of course. Against both is some extra weight, losing a litle of the ordinary bike qualities.
The Comfort ST has the extra frame rigidity which is good since the standard frame does have some flexing, but there's even more extra weight. One thing I inadvertantly omitted above is that the ST version has a full chaincase, which is a pain if the wheel needs to be removed, it's not the best implementation of that feature.
The performance is similar apart from the gear differences, so the rest is personal choice on the features you value.