Just so know that CTMH cardstock is thinnest of all you mentioned and it is white core. I love CTMH products and i am in a monthly club but I do not buy their cardstock. It is not for paper projects and you cannot do alot of layers on cards when using it for a base. --BUT it is perfect for scrpabooking.
PTI & GinaK are the heaviest cardstocks. They do have comparable colors to SU. Both of these companies have white cardstock that is awesome! I use nothing else on my cards. It is also heavy enought o use as bases.
SU does have the largest colorway though.
Check out this site as there are all the comparisons of colors for PTI & SU
http://www.flickr.com/photos/3865122...7623826086942/