Sketchbook styles

After running some errands, I treated myself to breakfast out on Wednesday and made two paintings from the experience. One was what I usually do when out in public, which was a fairly precise pen drawing of someone(s) sitting nearby, in my purse-sized sketchbook with watercolor added afterwards. The second was a snapshot of part of the table in front of me (I finished my omelet, got rid of the plate, and then painted what was left), and it's paint-only—no underdrawing, kind of messy, but more realistic.

So the question is...do I prefer one? Do others prefer a particular style? Where should I invest my time and effort?

And of course there is a third alternative, which is to make a more careful painting by choosing to do a pencil underdrawing that gets all the proportions just so, and on watercolor paper instead of in a sketchbook. Again, where should the effort be placed?

You can also see this latter piece on my book review blog tomorrow, to accompany a review of Behind Closed Doors, by B. A. Paris.