Recently I was looking at the website of the artist/illustrator
Kinuko Y Craft, who likes to work on a small scale with very fine detail (often using 00 size brushes). She mentioned that she uses Claybord pre-prepared panels as her support. Made by Ampersand, they have a very smooth surface, making them suitable for miniatures and fine work. The clay provides an absorbent surface that takes paint well.
If your aim is to produce a hyper-real image, you don't want a textured support that draws attention to to the surface and destroys the illusion of depth. But for plein air work, surface textures such as the brush marks of un-sanded priming, can add interest, energy, and a kind of honesty.
To get this level of smoothness with home-prepared supports would take a lot of sanding of multiple coats of primer or gesso, waiting for each coat to dry. Some might find the surface too smooth for their style of painting. I have yet to try them myself. Would welcome comments from those who have.
The panels, which are supposedly more archival than masonite, are also made with a box-like cradle suitable for hanging unframed (you might have to clean up the edges for presentability if you are a messy painter). The sides are also paintable. They are not cheap, but if you don't want to spend time preparing panels, they might be a good option, and you can save on framing costs if you use the deep cradled panels and hang them unframed for a clean, modern look.
The thin un-boxed panels would be the most convenient for plein air trips. Plein air painters often use slotted boxes to separate wet panels during transportation.
