The Goth most likely came from (eastern)Götaland and Gotland, it is strongly hinted at by similarities in material culture between the Island of Gotland, eastern Götaland and the Vistula basin in the first century when a Scandinavian material culture (the Wielbark culture) had suddenly replaced the preceeding material culture (the Oksywie culture). More specifically, what makes a Gotlandic or Götlandic origin more likely is the burials; stone circles and bautastones are otherwise only known from Gotland and Götaland but they show up in the vistula basin at the same time as we would expect the Goths to have lived in the area (along with other east germanic peoples like Rugians, Heruli and Vandals obviously, so It is ofc possible that it was some of theese other tribes that came from Gotland and/or Götaland).
Then we have etymological evidence, Gautar (Old norse for Geats), Gutar (name for the inhabitants on the island of Gotland) and Gutans (Goths in Gothic) all share the same etymological root, the protogermanic "Gutô" meaning "to pour". So they had the same origin, if a Geat and a Goth would have met before proto germanic started to split they would have called themselves by the exact same word. This strongly indicates that all three populations are connected.
Then there is linguistic evidence, Gutnish have some characteristics in common with Gothic that are unusual in other germanic languages, but theese similarities are not in themselves very strong indicators.
And then there is historic evidence, Jordanes history of the goths from 551 AD tells of how the Goths originally came on three ships from Scandza (Scandinavia) to Gothiscandza (which is probably identical to the concept of Hreiðgotaland in the norse sagas, Hreiðgotaland being an area corresponding to northern Poland), and as crazy the story becomes from that point on it still shows fascinating similarities with Gutasaga which tells of how Gutar in some distant past emigrated across the sea and ended up in the land of the Greeks. Now someone might say that the writers of the Gutasaga would have known of Jordanes account, but that is a hard case to argue in favour of considering that the getica was rediscovered (1442) by western historians about about 90 years after Gutasaga was first written down (about 1350), making it unlikely that the local priests on Gotland would have known about the Getica.
All things put together, the Goths most likely came from what is modern day Sweden, if we had a time machine I would bet money on it.