I found this article useful.
My own experience with small groups runs back to the early 1970’s, over 50 years.
Personally I am most impacted by actual Bible Study Groups, which allow for discussion around full Books of the Bible. I prefer to just use the Bible, my version is the KJV. Useful tools include two older commentaries Old John Gill’s, which breaks down most verses into phrases, and Matthew Henry’s. I also use a Bible app, and prefer the simple e-Sword, with easy access to the commentary, Greek and Hebrew text and definitions (having never studied the languages themselves formally, I rely on the dictionaries) and the extensive KJC, word Concordance, as well as just a general English word search 🔍 tool.
Actual Bible studies, allow one to discuss passages at a level that doesn’t get directly done by just listening to a sermon preached.
Studies of Confessions and Catechisms can supplement actual Bible Studies. I would add that if you have an effective pastor who teaches through scripture, having a Bible Study following their Sermons can be doubly useful. I have at least three pastors who I’ve used their material extensively. Unfortunately not the ones at my own church.
I rarely use contemporary books as the basis of my small groups. But at time we have read through older classics from authors like Bunyan, Wylie, Ryle, etc.
Here is the article to spurred this post.
Rainbow Trout 