Well, I think there are two categories here.
1) Impact to the photographic industry as a whole. I.e. a camera that has somehow impacted how the market sees m43 or cameras as a whole.
and
2) Classic: or a camera that is deemed a classic for M43 but not necessarily impactful to the industry as a whole.
According to
Impact:
Panasonic G1: only because it's what started M43 and put M43 on the world stage even though it didn't 'do' much. More like a foot in the door.
Panasonic GH1: Only because videographers gave pause to at least notice its existence, albeit I don't think it sold 'that' well.
Panasonic GH2: The camera that had caught the eyes of all videographers, budding video enthusiasts, budding filmmakers etc. The one landmark camera that put M43 on the map and caused everyone interested in video to consider. Specially when it's hacking abilities was introduced.
Olympus E-M5: The one M43 camera that caught the eyes of normal photographers and practically caused the start of the whole retro camera craze (well, I think E-M5 was the one that started it...was there another camera?). From a stills photography standpoint, the one camera that everyone equates M43 too.
Panasonic GH4 (and possibly GH5): 4K to the masses with 4.2.2. Basically, the camera that is so far ahead in features (for its price point) that cause all other manufacturers to give chase (albeit, Sony has done a stunning job of catching up since).
Classics
Panasonic GF1: the first and possibly the only true classic M43 camera produced by Panasonic. Small and stacked chock full of features (in it's time) including the, now classic, 20mm 1.7 lens. The one M43 that was considered the poor mans Leica when it came out. The epitome of what M43 stands for (well, in general terms anyhow).
Olympus E-P1 + E-P2: E-P1 was the one that started Olympus on M43 and it was a beauty. The first to start the Olympus IBIS fame (there were other cameras that had IBIS). Small sleek with decent features. Unfortunately rather pokey in AF (albeit, that was helped by rather unimpressive kit lens though it did have one redeeming feature...it's collapsible ingenuity). E-P2 only because it fixed a number of problems E-P1 had...mainly the lack of EVF (albeit, optional EVF).
Panasonic GH2: Most famous Panasonic M43 camera from the perspective of videographers.
Olympus E-M5: Most famous M43 camera was impactfull and was a classic.
Panasonic GM1/5: Well, not sure if this should be in here but it "IS" the tiniest M43 camera ever with build quality that exceeded expectations (and priced accordingly too high to be sold in great numbers). Besides, probably a bit too early to be considered a classic.
Honorable mention:
Olympus E-PL1: from a budget camera point of view, it did really well I think. If it had sold enough that it had put M43 on everyones mind, i.e. a modern day Kodak Brownie, then it would instantly go in the Impact and Classic section but sadly it didn't do nearly enough. Still, was a best seller I believe (albeit, when it went on a fire-sale), at least from an M43 standpoint.
Olympus E-M1: was sorta overshadowed by E-M5 and was a slight let down ONLY because E-M5 was such a significant model which the E-M1 just couldn't catch up too even though technically it was in another category all together.
Olympus Pen-F: Would probably be a classic but it was one of those gorgeously crafted items that everyone lusted for but hardly anyone bought, mainly because of price (although it's target of JPG shooters may also have had impact).
Dishonorable mention:
Complete and utter lack of marketing from Panasonic
Oh, and the Panasonic G10. The one camera that was deemed a complete and utter failure. What the heck were they thinking?
--
Hubert
My non-digital gear: Agfa Isolette, Ricohflex VII, Bessa R, Bessa L, Zorky 4, Fed 2, Konica Big Mini, Konica Auto S2, K1000, Yashica Electro 35 GX, Recesky
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