OBD: Fast, no disassembly, low risk. Use when the ECU supports full OBD read/write.
Bench: Full access regardless of OBD protection. Requires disassembly and correct pinout knowledge.
BDM / JTAG / BSL: Access to everything. Highest risk — power interruption can leave ECU unrecoverable.
The default rule: Try OBD first. If protected, go to bench. BDM only when no other option.
This decision tree is the first chapter of Safety ECU Read/Write.