Add a second ISP with tracked defaults or BGP multihoming

A 400-person company has one 1 Gbps internet circuit from ISP1 on edge router R1. ISP1 also assigned it 192.0.2.32/28 for public services. A contract for a second circuit from ISP2 is signed. The CIO says: "Add the second ISP so we never go down again." You are asked to choose the design and defend it.