I spent six years from start to finish on each of them, with some overlap when I put the first aside to attempt to find a publisher. Poured everything I had into them, and then moved on. I read The Greatest Show on Dirt a couple of years ago, just to refresh my memory on what I had written. It will always have a special place in my writer's heart, having been my first, but reading back through it confirmed to me that it's not my best, even though it has sold better than all of my others.
No, my best book, in my opinion, is Nine Bucks a Pound. Though four years after its release, I seemed to have forgotten most of the nitty gritty details and could only answer my uncle's questions to the best my fuzzy memory would allow. Which was made the worse by the humdinger of a cold settling into my head the night I saw him. Later that week, when I finished the book I had been reading, I decided it was time to dust Nine Bucks off and give it another go.
