Polaroid Originals is bringing back as much as they can, but it's easy to see from their website that their focus is on the 600 type film. But, here's the difference:

600 Type Film - 3.1" x 3.1" Image area. ISO 640 film. Produced in Color and Black and White, with white borders or color borders. Also now produced in a "duochrome" - a black and white film with a blue or pink color overlay. Will work with older 600 type cameras and the newly made I-Type cameras.

SX-70 Film - 3.1" x 3.1" Image Area. ISO 160 film. Produced in Color and Black and White. Will work with older SX-70 cameras. I have no experience with these films (as my instants are Fuji) - but I would assume the SX-70 film to be more vibrant and saturated due to the lower ISO.

I-Type Film - 3.1" x 3.1" Image Area. ISO 640 film. Same exact film as the 600 Film. The older Polaroid 600 cameras were powered by a battery that was stored in the film pack. The new I-Type cameras have their own power supply, so they do not need to use this battery. The I-Type Film packs omit the battery - saving a few bucks on their price. This film will only work with I-Type Cameras.

Spectra Film - 3.5" x 2.9" Image Area. ISO 640 film. Same chemical formula as the 600 Film, but in a wide format. Will only work with Spectra Type Cameras.

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Boiling it down:

There are only 2 color formulas - the ISO 640 formula, and the ISO 160 formula. You'll need a SX-70 Camera to shoot the ISO 160 formula.

If you want to shoot W I D E - then you'll need the Spectra Camera.

And if you want to shoot the good ol' fashioned polaroid - then a new I-Type Camera is the way to go, as it can shoot the less expensive I-Type Film and all variations of the 600 Type Film.

Also in this market are cameras designed to shoot Fuji's Instax film, of which there are square, mini, and wide versions. The mini film has quite a few novelty versions. Cameras for these include those made by Fuji and Lomography.

more specifically (for anyone interested) I'm thinking about buying a SX-70 or a Spectra in stead the 600 camera I'm currently borrowing, if the film quality/results are better, since the current prize differences between films wouldn't really matter for my use.

Instant cameras are novelties - they're fun to use and toss the images onto the fridge, in a scrapbook, or mail to someone. My Lomo'Instant Wide isn't really that sharp and it vignettes like an 80's glamour shot - but it's got character and I like the wide film. In choosing an instant camera - "Image Quality" is fairly unimportant. Pick which format or film styles appeal to you the most instead.