I think whenever we buy something, then we are using Bitcoin as currency. But when we're just holding on to them and we leave them untouched, then we use Bitcoin as an investment. My answer to this question is both. I use bitcoin as currency and I also use it as an investment. I have bought some stuffs online using Bitcoin and I'm currently holding on as much bitcoin as I could so that after a year or two, I could get my profits.
it's as following.
currency aspect: when you buy and sell stuff, send and receive transactions from any level.
investment aspect: when you use it for trading purposes, buying it to hold it for a certain period to sell them later on.
store of value: keeping a good portion of your money in bitcoin for a long period of time. of course this can also be seen as some sort of investment, but a lot people don't treat it as such as their only intention is to keep money out the banking system etc.
these are 3 aspect of bitcoin that i am using.
I mainly use the investment and store of value part. I hold 90% of the bitcoins I bought. I also spend some bitcoins.