During my watercolor adventures, I've utilized a number of different brands and types of watercolor paper. The quality, sizing and texture play a huge role in the kinds of effects achievable with the watercolor medium. I've learned to stay away from hot press papers, they may be fine for intricate, positive shape filling type art but do not allow for the time necessary for the intermingling of hues. Cold press is better but my choice is always the "rough" type texture. I love how you can deftly pull your brush across the tops of the ridges to create fragmented light effects.
The sizing ratio is also very important. Too little sizing or old paper where the sizing as dried out of the paper is also problematic. I've done class demos on old paper only to create a big blotchy mess in front of my students.
My go to paper is the Arches, rough style...I only use 140 lb. paper, I've seen little need for the 300 lb. heavy weight paper however, I can see where this might be a good choice for larger works. My pigment and water mixtures interact predictably with the gum arabic ( and other chemistry) sizing percentages in this paper.
The following painting however, was done on a brand named, Saunders (Rough, 140#). I've discovered that this brand acts quite differently than my Arches paper. I will compare my experiences with this paper in the following set of sequential steps in my painting "Valentines Day".. Enjoy!