Here are FBS conferences, ranked by average SP+:
1. SEC: 14.8 average adjusted points per game (33.0 offense, 19.2 defense)
2. Big Ten: 6.6 average (26.9 offense, 20.5 defense)
3. ACC: 5.2 average (30.2 offense, 25.1 average)
4. Big 12: 4.5 average (29.7 offense, 25.4 defense)
5. Sun Belt: -6.4 average (25.3 offense, 31.7 defense)
6. AAC: -7.3 average (25.6 offense, 33.0 defense)
7. Mountain West: -8.2 average (24.3 offense, 31.6 defense)
8. MAC: -12.6 average (18.7 offense, 32.1 defense)
9. Conference USA: -13.8 average (18.7 offense, 32.1 defense)
The SBC has been the top G5 for the last 3 years or so.