I can't agree more. All the others mean something different.

"I couldn't agree more" or "I couldn't agree with you more" is better to say. You could also say "I completely agree."

if my translation of your chinese characters were correct, what you are trying to say is ,"i totally agree" if in that case i am correct,then i think it's best to say "i couldn't agree more." - this means i support you very strongly. "i can't agree with you anymore" means i can't support you with that thinking/fact/matter anymore

A little bit of help on the grammar of "agree" here. I agree (with you) a lot. I agree a little. I agree only 50% I agree 100% I don't agree totally. (= not 100%) I can't agree more. Rule: agree + how much you agree Geddit?