I usually paint on either
canvas covered panel,
or stretched white cotton canvas.
Of the three I prefer the canvas covered panel. I like a firm surface and the weave is close on the canvas so it's quite a gentle support and allows for detail if I feel so inclined.
But last week I bought some linen canvases mainly because Great Art, whose catalogue I take to bed to read, has a deal on. So I bought 4 of 30 x 30 cms.