What is the best to straightening my hair?

My hair is long, thick, and wavy at the very top, near my scalp. the rest of my hair is "straight" but it frizzies in like 30 minutes and when i wear it down it doesn't look straight, and each one of my hairs is thin so they burn easy. What is the best straightener for me to get to make my hair perfectly straight? I've had a few straighteners before but they only made it worse, I've heard the chi is good, but are there any better ones for my hair?