I agree with you 是人们最常用的表达方式。
两者含义和用法相同。"I agree with you" 比较口语化，很常用。"I am in agreement with you" 则多用于更正式的场合。
I agree with you that everything seems to be getting worse in this town.
I know if might not seem like it, but I agree with you 100%.
Did I tell you that I agree with you about these decisions?
Oh, believe me--I agree with you that we need to do more to fix this place up.
I agree with you on the first point, but I disagree on the second.
I do not agree with you on this issue.
I think that I agree with you, for sure.
I do agree with you about some things some of the time, even if we disagree on most things most of the time.
I am in agreement with you about how to move forward on this issue.
Did she tell you that I am in agreement with you?
I am in complete agreement with you on this decision, captain. We should definitely head east.
I am in agreement with your decision about how to deal with this mess we created.
Are you in agreement with the rest of the men onboard?
I am in agreement with you: we do need a new desk.
I said that I am in agreement with you about most of these topics.
He is in agreement with me that the new refrigerator is much nicer than the old one.
I am in agreement with you as usual.