I personally.... and after advising with friends....do not think it matters. I didn't see any difference in the cool alert or the learning designs. My son just turned 3 when he potty trained fully and I don't think he even noticed the coolness....maybe he liked it :). I know it didn't make a difference in his training.
I put water in one once and noticed the coolness immediately. I think if he is in it longer than one pee ("Wee" all do it!!) than it really isn't working how huggies wants it to.
I am a generic diaper user....but I refused the generics with pull-ups! Huggies is the best in my opinion because they are the only ones that have velcro sides. I thought it was essential to not change my son "like a baby" and the velcro side sure did help me not to have to take clothes off and on.
I personally just let him pick the one he liked and we talked to him about not peeing on Mater or Lightning! But, I will tell you...when I mustered the courage to just take away the pull-ups and put him in real underwear all the time (despite the accidents and frequent trips to the washer) it made all the difference in the world!!
Good luck! Hope I am of some help!!!
K.
(Mom to Riley 3 and Tyler almost 2...and already pottying!!!)