I've competed in several AtCoder Grand Contests (AGC) and have noticed that my performance in those is much worse than in Codeforces Div. 2 contests. Moreover, I find the problems in AGCs on average much more interesting than those that show up in Div. 2 contests. I want to improve at AGCs specifically, and I was wondering if there were specific websites/sources of problems to train on that have the most overlap with AGC-style problems. So far, I've come up with the following:

-Practice previous AGCs -AtCoder Regular Contest -TopCoder (problems tend to be more math/thinking and less implementation heavy than Codeforces)

What are your thoughts on the above three sources, and do you know of any others that would serve as good practice for AGCs?