I have a few favorites, and sometimes combine them.
#1: Watercolor paper (I use Arches 140 lb) with reinkers (SU & Adirondack) & waterbrush (Niji).
#2: Copic Markers on Georgia Pacific White Cardstock (From WalMart)
#3: SU Markers & Niji Waterbrush on Watercolor Paper
#4: SU Classic Pads (ink squeezed into the lid) & Niji Waterbrush on Watercolor Paper.
I usually combine all 3 techniques when watercoloring.