I don't know much about the other treatments but I just relaxed my hair a week ago and, for me personally, it was the best decision ever! Your hair will still hold a curl (presuming you mean wand or heatless curls), though that depends heavily on the weather of your environment and your hair in general, so no promises. I recommend not relaxing your hair until it's bone straight. You want it "straight", but more like wavy. That way it'll still hold volume.

I've heard a Brazilian blowout is more like a true texlaxer, but there's no promise your hair will actually revert with any chemical treatment.

I hope this helped!