What is the difference between lines such as 电信, dual-line, and multi-line? How should one choose?

Single-line means it only supports 联通 or 电信 lines (currently, interconnection between 电信 and 联通 has improved somewhat), dual-line means it simultaneously supports 联通 and 电信 lines, and multi-line BGP data centers support more lines, including the former 铁通, 移动, etc.

Prices vary for different lines. Choose whichever line your website's users primarily use. If user coverage is broad, it is recommended to choose a multi-line BGP data center.