Splaash,
The Leica II ( referred to in some books as model D ) was introduced in 1932 as Leitz's first 35 mm camera with an integral, coupled rangefinder. It was an advancement over the Leica Standard and Model I cameras.
It was joined by the Leica III in 1933 which added "slow" shutter speeds from 1 sec to 1/20 sec via a knob on the front of the body.
Alpha suffixes identified subsequent refinements of all models of thread-mount Leica ( I, II, and III ).
The -a suffix models added a top-shutter speed of 1/1000.
The -b suffix placed the Viewfinder and Rangefinder windows right next to each other.
The -c suffix models had an all-new body made from an aluminum casting, offering greater stregnth and stability, plus improvements to the shutter mechanism.
The -f-suffix models were the first Leicas to offer integral flash synchronisation, and came in two flavors: "black-dial" and "red-dial" (referring the the flash sync).
The III-g was the last, and many believe the best, refinement of the thread-mount Leica: it featured a larger & brighter viewfinder window (but still two separate eyepieces for VF and RF), as well as bright framelines w/ parallax compensation when focusing for the 50mm and 90 mm lenses. And a built-in self-timer. And flash sync was now automatic, no more fussy sync dial and guide-book.
The III-g is pricey, with decent bodies averaging $700-$900 USD, up to $1,200-$1,500 (or more )with a lens... many argue that with even with all the improved features, it's still not as good a camera as the M-3, for nearly the same cost.
The III variants are good cameras, some late -c and early -f models tend to have issues with poor chrome and deteriorating shutter curtains, due to materials issues following WW II. If you don't have a need for the slow-speeds below 1/20 second, then you probably don't "need" a III.
The II are the basic LTM camera w/o the slow speeds. They still have "Time" and "Bulb" settings, and the -f models are flash-synched.
The black-paint versions usually bring more money, especially if the paint is in good to excellent condition...
Black-paint cameras or very early serial numbers that were sent-back to be upgraded aside, Model II generally run a little cheaper than Model III cameras, generally $50-$150 USD difference.
Black-paint and low-serial number Leicas are generally considered more desirable as collector's items than as daily users, mostly from the standpoint of wear and tear diminishing their collector value.
If a user camera is what you're after, I would suggest looking for a clean II-c or II-f, but would not suggest passing-up a III-c or III-f if it fit your budget.
Hope this helps sort it out a bit , I hope I haven't gotten my Leica history muddled !
Regards,
Luddite Frank
