The GOOSE set seems to be fairly uniform in most accent, but mine has quite a bit of allophonic variation. As far as I can tell, there are three realisations: a diphthongized one after alveolars eg. tune [ts1un]; a fronted and slightly diphthongized one after /j/ eg. few [fj}u], and my regular back one eg. goose [gus]. It also produces variation in consonants, but I haven't entirely figured it out. A few words, like 'Tuesday' ["tS1uz.de] and 'during' [dZ3`r\IN] have post-alveolar affricates, but most seem to have alveolar ones, like 'tune' or 'dune' [dz1un]. What sort of variation within this set exists in other accents?
GOOSE set
I have mentioned this before, but for the purposes of this thread I should note that in my dialect I have diphthongization of back vowels after coronals so that they have centralized or even fronted onglides, and out of the back vowels, /u/ diphthongizes most markedly, especially after /t/ and /d/. Consequently, when spoken stressedly, /u/ may even become [yu], especially in /tu/ and /du/, even though in less stressed speech it more often becomes [}u]. Such makes it sound as if a yod is present even though such is not at all related to historical yods in English from Middle English /iu/, /eu/, and /y/.
I don't think I have much allophonic variation in the GOOSE set: I have a very narrow diphthong [Uu] in all positions. (The onset of this diphthong is fully back, as opposed to my [U] in "foot", which is near-back.) For the sake of simplicity and convention, I usually just transcribe this diphthong as [u:].