ComArt paints were originally designed for illustrator artists. That's why they're so thin. As you said, numerous colors available in opaques and transparents. I use them primarily for weathering and shading. I definitiely wouldn't recommned them for base coats. Some of the tricks I've picked up when dealing with ComArt is to build up the colors up slowly. I either put a couple of drops of Future or Dullcoat in with the paint to give it more "tooth" and always seal between coats.I just recently picked up some ComArt airbrush paints from Tom Grossman and I can't say too much yet. I have only used them a couple of times so far and noted they spray very well but almost seem too thin. While that makes them spray well they run easier and it takes more coats to cover. But as I said, I have very little use and shouldn't make any judgements yet. I bought them in sets for things like horror figure models and other things. The color selection is nice and I plan on putting these to more use soon.
I love AV Model Air paints. They flow very nice and dry rock-hard! Plenty of colors too.