From what I've read about modules so far, I still prefer using dep over it. Sure the GOPATH issue can be annoying but a tool like venv could be developed to mitigate that and in practice at my day job, only having 1 GOPATH has never caused me any issues with dep.
I personally found vendoring the external libraries into “/vendor” was quite useful to be able to explore/read the code that was being used. I find it odd that isn’t default behavior.