Like it's even possible to notice.
I will say one thing about Tokina though: Worst chromatic abberation and best build quality. That's what they're famous for. Sigma, good build quality and good optical quality lenses. Tamron's lenses are usually sharp (and sometimes sharper than Canon and Nikon equivalents), but they feel the cheapest. For many people, it doesn't matter. Plastic lenses will last as long as metal lenses under normal use by most people. Plastics are quite strong and durable nowadays.
I realise it is the person behind the camera that makes all the difference. It is the quality problems I am worried about. And rightly so. I work hard for my money I want to get the best value for it. If you are paying $500 for an item and you have a choice of two items one with a 10% chance of failure and the other with a 25% chance of failure which would you chose?