Best way to learn vocabulary?

I’m using Torii also developed by a WKer: Torii - SRS learning application for vocabulary

I really like it; it is incredibly similar to WK, and you can even order vocab by WK kanji level and it just the other day got new features (so it is actively developed). It is free and will stay free (as far as I know). If you want to be able to add a lot of your own vocabulary, then you’d need to pay a little, but to me the prices look more tip sized than anything. I’m planing to chip in some money soon now that I’ve used it for a while and really like it.