either of those will work, or, as I do it, just use several ace bandages to flatten your chest out. (getting a friend to help with this is the most successful. Do it over a sports bra and then 'divide and conquer')
It's sort of up to personal preferance and boobs. Certian boobs work better with certian methods. Whatever you choose you need to practice with it. It's like people who wear heels for the first time to a convention. It ends up looking uncomfortable and it feels worse. You need to put it on and wear it a fair bit to get used to it before you try wearing it for longer periods of time.
If it's too tight it's going to be very uncomfortable and painful, and if it's not tight enough it won't work. If it's the right size and you have enough practice your body will get used to breathing in the top of your lungs and it'll actually feel plenty comfortable. It might chafe a little but it shouldn't hurt.
Again, it's hard to say what will work for you since ever body is different. If I were you I'd try to start with ace bandage if just to get the feel of it. If you decide that you don't like how that looks you can move on to the binder shirts.
Good luck!