"I would rather feel painful than feel empty."
Translation:Tôi thà cảm thấy đau đớn còn hơn cảm thấy trống rỗng.
I think this should be "I would rather feel pain". Pain is a noun, whereas painful is an adjective describing something which is causing pain. It's a bit complicated, though, as it is not always incorrect to use an adjective without a noun after the verb to feel: we can say "I feel joyful", for example. However, I have never heard anyone say "I feel painful". We might say someone is a painful person, meaning that they cause discomfort, but I don't think it sounds correct to say "I would rather feel painful". The sentence suggests you feel like you'd rather be the cause of pain, whereas I think it means "I would rather feel pain" as in feel hurt.
"Thà" means you would do something bad rather than do something worse. This sentence is an example.