If your friend is sick, which would you choose: "Get well" or "Be well"? And if you use neither of them, what do you personally use?
"Get well" is appropriate. To me, however, the phrase is something that would be written, for example in a "get well" card. It is a little too cliche for me to say in an everyday conversation.
On the other hand, "Be well" is usually an informal way to say, "Goodbye," (like "Peace" or "Later") and does not have the same meaning as "get well."
I think "get well" implies that the person is not well now and needs to become well, whereas "be well" implies that the person is well and can continue being well.
I personally would most likely say, "(I) Hope you feel better" or simply "Feel better." This is entirely a personal choice.
Tradition dictates that the phrase in its entirety be:
Get well soon.
See Google images
As Scotty correctly pointed out, it has become bit of a cliché, so I have often wished a sick friend or relative of mine
A speedy recovery or I hope you get better soon! They both have the same meaning.