The 66 was the best of the range by far as it had a superb dome mid as well as really good bass and top. It was a very good speaker by any standard. The next down was the 44, a really nice 3-way, but lacks a little clarity compared to the 66. The 33 and 22 were bass-compromised versions of the 44 and rather less successful. The 15 was kind of the default speaker of the 1970s, very affordable and very well thought-out. It could sound a bit woolly and loose in the context it was sold due to the limitations of cheap record decks, but with a good source it is really rather good. Not the last word in detail or speed, but very easy to listen to across genres. The oddity of the range was the Ditton 25 which is kind of a giant 15, i.e. a two way but with 12” bass drivers rather than 8” and a reputation for not much mid-band!
The sleeper here is there is a B&O speaker that is basically Ditton 66 parts in a smaller cab, i.e. it has the superb dome mid. I can’t remember the model number, but they go for about half the price or less of a pair of 66. Adam (Beobloke) will know it for sure.
Basically I’d rate them 66, B&O, 44, and I do have a soft spot for the 15 as it was just everywhere at one time, I knew a lot of people with say a PL12D, little Marantz or Pioneer receiver and a pair. They just remind me of growing up in the ‘70s!