One member of my writer's group, the Tower Poets, devoted a year of her life to writing one sonnet a day. The sonnet seemed to be her favorite form, and from her prolific output in that form, she seemed to accomplish her objective.
My favorite western form is the triolet. While much of my published poems are Japanese short form, there is something I also enjoy about the triolet. For one thing, a resourceful poet can use that form to repurpose a free verse poem that can't seem to get there. Perhaps the poet likes several lines from the poem and considers it to have potential, but they just can't seem to revise it to the point where it works for them and seems ready for querying. But all you need are two good lines to begin a triolet! A resourceful poet can salvage the strong lines from a weak poem and position them as line one and two of the triolet. Below is an example triolet opening from my poem "The Weed-Filled Path"