Hmm... now that you mention it, I never use either word when talking to people.

I don't use "invest" because I don't see it in the same class as other investment vehicles, like stocks or real estate. Investment implies some centrally directed venture by which you hope to earn a return, but Bitcoin is more of a movement than a venture.

I also don't use "save" because it just feels weird to use the word "save" in the context of buying something. But "save" is probably more accurate.

The words I usually use are "I do recommend putting some money in Bitcoin" or "It's wise to keep Bitcoin as part of your portfolio".