I quite agree with your opinion.
Personally I tend to agree with your opinion.
两个都可以。
表示同意他人意见
So do I. 我也这样认为。
I agree (with you) completely / entirely. 我完全认同。
I can’t agree with you anymore. 我非常同意你说的。
I feel the same way. 我有同样的想法。
Exactly/ Of course. 表示绝对、当然