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In comparison to the canoes you remember, you said you are looking for a "light smaller boat that might be at least a little more fun". Well, SOTs will NOT be smaller or lighter than an "appropriate" solo canoe. There are lots of very sporty, "fun" solo canoes, many of which weigh about one-third of what a SOT does, and even the worst of them will not weigh more than two-thirds of what a SOT weighs (Okay, I should mention that both Mad River and Old Town make some small canoes that are roto-molded and weigh the same as a SOT, but those monstrosities really bear no resemblance to canoes, in my opinion). The initial part of the learning curve for paddling a solo canoe is a bit more challenging than that of a SOT (or rec kayak or touring kayak), but if that doesn't scare you and if a solo canoe is appropriate for your expected usage, don't rule out that option.
Here, a picture is worth a thousand words. The average person who remember canoes from their younger days as big, clumsy and slow doesn't realize they need not be like that, even solo, and likely won't picture a solo paddler making this kind of progress when paddling with moderate effort against the stiff current of a river in flood (the first clip is typical, and the second shows failure to see a bit of cross-wise current soon enough to react gracefully):
Oh, accidental paddle contact with the boat sounds really kutzy here and doesn't support the paddling image I wished to convey, but that's because the camera, being clamped to the boat, picked up every little bump and creak of the hull and amplified it. Even the swishing of the water was far more quiet, relative to background noises, than what's heard here.
All mine are, including a SOT of the fourteen canoes and kayaks that we have.
If you want one get it.
There are some super fast sleek ones along with the big barges, and the surf ones.
... the rest of the OP's remarks seem to indicate an interest in where they are on the spectrum of efficient function, which really clarifies his use of the word "toy". It sounds like he wishes to avoid something that's heavy and sluggish. Rather than get get too hung up on the terminology, I think people should address the true meaning of the question (or ask for clarification if needed).
There are some truly high-performance SOTs, but they tend not to go by that name (surf skis) and they aren't practical for most people. Some are middle-of-the road but these are usually heavy. Plenty more really ARE low on the performance scale. There's lots of potential for discussion here but not many are going for it (I can't because I don't know many models).
A sit-on-top can be very sleek, fast and narrow
They can also be very wide barges that float
as some of the fishing platforms represent.
Malibu Stealth 14 Fishing Kayak