The two are effectively one and the same as riverplate.com.ar redirects to the first link.
I'm only on dial-up and whilst the first site is relatively media rich, it didn't take long to load and I noticed no spike in system resources. It also has a number of cross site scripting which can also slow loading and or increase resource use as that will also be monitored.
I use firefox 3.5.7 with NoScript which blocks scripts by default (temp allowed cariverplate.com.ar) and also RequestPolicy (blocks cross site access unless allowed) add-ons, so thes may also have improved my experience.
What browser/s are you using and is this the same and is the same across all browsers ?
What other security software do you have installed ?