If maximum availability is the top priority, we generally recommend using Provider A as the primary SIM and Provider B as the fallback SIM. This reduces the risk of both cards being affected by the same network outage or backend issues.
If, on the other hand, costs or internal requirements play a greater role, a more cost-effective primary plan paired with a robust secondary plan may be a sensible choice. For industrial applications, we generally recommend using only M2M SIMs, as these are designed for long-term operation and higher resilience. Ultimately, the deciding factor is whether your priority lies more with availability, cost control, or clear provider and security requirements.