Probably the most popular format but also the last film to be mass produced, it brought highly portable photography to the masses in the 1950's and 60's surpassing 120 roll film in a fairly major way. Iconic cameras such as the Nikon F and the Olympus OM1 were owned and used by as many professionals as they were amateurs. My personal favourites were Kodachrome 25 & 64 positive emulsions - sadly no longer available.
Introduced by Kodak in 1901 for their famous box brownie, this film was going to set the bar for quality, ease of use and image quality. 120 roll film remains popular and highly usable medium to this day for the above mentioned reasons. I currently shoot with several medium format film cameras and the beauty of 120 is it can serve them all 6x4.5cm, 6x6cm, 6x7cm & 6x9cm all with one film stock.
5" x 4" Large Format
5x4 is the most popular large format film type but 10 x 8 is also very popular too offering outrageous image quality. More complex to load and shoot and of course develop it is the ultimate in quality from film. The large format photographer is a special breed that's for sure, but it makes you slow down and be extremely diligent with your exposures, the work flow taking on a whole new format.