A1 and B1 have lower peak brightness than C1. Also the CPU is mediatek not LG's custom SoC.
I have a 48" A1 in the bedroom where it works great and I got a really crazy deal on it. However as a primary TV, it is better to get a C1 or G1.
A1 only supports 4k60 and its ports are HDMI 2.0. Not sure about B1 but C1 definitely supports 4k120 and has 40Gbps HDMI 2.1 ports.