The phonology of English shows extensive variance among its multitude of dialects. Which phoneme(s) shows the most variance throughout the language?
I think the most immediately apparent choice would be /r/: [ɹ], [ɻ], [ɾ], [r], [ʋ], [ɹ̈] (bunched molar), and [ʁ] (quite rare now I think) all exist. That isn’t even considering secondary articulations - like velarization and labialization - or nonrhoticity. Alternatively, the frontrunner which seems promising to me is the GOAT vowel - often broadly transcribed as either /əʊ/, /oʊ/, or /o/. Depending on a speaker’s accent, the vowel can be realized either as a monophthong or as a diphthong ending in [ʊ̯], [u̯ ~ w], [ʉ̯], [ʏ̯], [ə̯], and possibly other qualities. The primary portion of the vowel can vary from [ə] to [o] to [ɤ] to [ɔ] to [ʌ] to [a] to [ɐ] to [ɘ] to possibly [ɛ] and everywhere in between (lol).
I would appreciate educated input into my inquiry. Alternatively, which phoneme has the least variance? I was thinking something like /m/, /f/, or /v/, perhaps - the only variant I know is [ɱ] which isn’t really specific to certain dialects.