Really shouldn't knock the GoFlex wifi devices to much if you haven't tried it. They are a really slick devices. The current one provides 1TB of storage, around 3-5 hours of power for wireless access, DLNA compliant, and accessiable via WIFI with a app to download, upload, and stream meadia. I am not sure about the newest version of it, but mine came with a Power adapter for my car. It is a great option to stream content for multiple devices and such.
I have a OTG cable as well. But it is far from perfect. First it either requires root or app to mount the media from it, and isn't writeable unless you are rooted. Plus then you have the issue of not being able to share the contents if you want to. Limited storage capacity based on what ever flash drive size you get.
It is really a bit about use case right. If it is just me I could be ok with the OTG cable, though not really keen on it dangling on the side, but once I consider my daughter there isn't any question.