20MHz
20/40MHz HT Above
20/40MHz HT Below
I should choose which？
Please help me

If I choose 20MHz Bandwidth Test TX+RX=100Mbps
If I choose 20/40MHz HT Above Bandwidth Test TX+RX=200Mbps
why?

40Mhz has more transmission room compared to 20Mhz so higher air rates and throughput. Dont forget SXT have only 10/100Tbase ethernet controller.

40Mhz has more transmission room compared to 20Mhz so higher air rates and throughput. Dont forget SXT have only 10/100Tbase ethernet controller.

On that second point, 200Mbps TX+RX isn't overkill with 100Mbps Ethernet: it means you can max out the cables at both ends simultaneously. Even with 10Mbps, the higher negotiated rate from the 40MHz channel isn't a total waste, as it allows more frequent opportunities to retransmit.