I think if you just pick either of DataFrames or DataTables and stick with it for a while you’ll be fine. My only caveat is that if you are dealing with datasets ≳5GB you might find the type stability issue in DataFrames to be an obstacle. I have a few simple tools for doing conversions in such in my DataUtils package which you can just copy over if you don’t want to rely on my package.
Edit: The one other thing I’ve forgotten about is the lack of something like the very nice DataFramesMeta, however @davidanthoff seems to have been working away furiously on Query.jl so I’d imagine that’s quite nice and compatible with lots of things by now. Like I said, the simplicity of DataFrames/DataTables has made it much easier to write simple tools, so I’ve actually found the simple things in my DataUtils package to be quite adequate most of the time.