As far as clam vs. swinger goes;
I'd say it simply comes down to personal preference. Both ultimately do the same job in the same manner in the same amount of time.
I like to 'get over' my shirts to visually line them up. I have my press on a 8 foot folding table and the swinger allows me to lean forward and try to see directly over the shirt.
It seems like a clam would make you have to work from the side a bit. I mean, do you clam owners find yourself standing in front of the press, but moving your head to one side or the other of the press to grab the shirt? Is the handle of the clam ever a issue?
And it seems like a clam has a greater vertical operating distance. Seems like you have to do more reaching up and down whereas a swinger makes your arm move in a easier horizontal motion.
For me, it's the swinger.