Over the years, both the Russian and American Big Muffs have gone through several design and sound changes. Currently, the American version being manufactured is modeled after the mid-70s/early-80s "NYC" model while the current Russian version is a new design in which the electronics are housed in a black box with Fender-style chickenhead knobs.
The earliest American Big Muff Pi which featured a triangular knob configuration and shiny metallic stomp box is the most expensive and sought after Muff, often going for upwards of $300 in good condition. After that, the "Ram's Head" Muff which featured the iconic Electro Harmonix ram's head crest prominently on the case commands the second most demand and attention. Originals of the "made in NYC" version are third, as they are more common than the other two by far. During the 1970s, Electro-Harmonix manufactured some one-off variations on the original Big Muff including the Little Big Muff and rare Big Muff Deluxe. Because of the oddball nature of these effects, many collectors are drawn to them.
Not to be outdone, the two earliest Sovtek/New Sensor models are consistently touted by many players as being the best in terms of sound. These are often deemed to be better for riffing than the American Big Muffs. The first Sovtek Big Muff Pi was housed in a tough, gray box with the knobs in a triangular formation. These models usually sport either green or blue ink on the top with a more highly stylized "Pi" symbol in place of the one that appeared on the American models. The other Sovtek Big Muffs apearing throughout the 1980's and 1990's were manufactured with many different design schemes. Some of these variations became cult favorites, especially the much sought after "green" models which many players, including Billy Corgan, swear by. The current Sovtek version on the market is housed in a black box with yellow type. Unlike their American counterparts, the Sovtek Big Muffs do not feature a true-bypass circuit off the shelf and must be modified to keep the unit from sucking tone when turned off.
The Double-Muff and English Muff'n are the newest variations on this classic stompbox that Electro-Harmonix offers