Yikes, I have too many "favorite" box forms. I guess if there are many, maybe the concept of favorite goes sideways.
I once made a composite of photos of some of my favorite boxes. Well, I included a couple that are a bit less favorite but still I like them better than some I've made! (Rather than throw those away I gave some to kids - they aren't very picky.)
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The three from black&white Ebony have threaded lids. One on bot right is a music box. Top center is a walnut box, a copy of the late Lisi Oland's favorite box, one her husband Knud Oland made so many decades ago (I photographed, measured and traced to try to get the shape right.) Knud's didn't have a lid - I don't know if the lid on mine is a plus or minus.
The one on tripod stand I call a pod box - I know of no box rules that say a box has to be able to sit on a flat surface. . I love the shapes of the Cocobolo boxes at top left and the African Blackwood at middle right. The insides of these are nearly egg-shaped.
The tiny boxes at upper right are sometimes made as needle cases or to carry pills. I've made dozens of different shapes but my favorite is the one with a bit of flare on the lid.
I'm not sure what to call the one from Albizia and brass on the lower left. I guess it's a lidded box since it has a lid but the lid is kind of unconventionally set down in a tapered section below the top rim. First time I tried that shape and I like the way it feels in my hand.
The two from American Ebony (Persimmon) at bottom middle were sort of an experiment. I like the shape, even the one with a rounded top. I did catch some grief from some who said that lid shape would make it hard to open. But it doesn't. I don't do boxes with the "woodturner's suction fit", IMO good primarily to impress other woodturners. My least favorite of these is the one with a greenish-blue cabochon - I dislike the wood, the shape with straight sides, and the color combination. Don't much like the one next to it, either. Live and learn.
If embarking on a box-making spree, consider making some large Beads of Courage boxes. Many clubs encourage these, made for children who are seriously ill, many with cancer. They get a special colored bead for each medical procedure, thread them on long strings. A BOC box gives them a place to store some of their strings of beads to pull out to tell their story. What's to like about these is more the reason for them. The size needs to be large enough to hold plenty of bead strings. The lid loose lid and won't stick with seasonal changes. A gentleman in our club keeps a cabinet at the local Children's Hospital stocked with as many boxes as he can get - a new patient can pick their favorite from the cabinet. Nothing else matters! However, I do like the shapes of those I made with the basswood layer so I could add chip carving. My least favorite shape is the one in the middle.
All of these are best made, I think, with a wide enough base so it doesn't tip over easily. The one at top right has a possibly undesirable feature of a thick lid with a tenon - but that's the only good way I could think of to fit a music box built into the lid. Made from a large, dry y.poplar blank.
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JKJ