If you're relying on public transport during your stay in Milan it'd be hard to beat Hotel Catalani e Madrid in terms of location; 2 metro stops from Central Station.
This small and cosy hotel provides clean and comfortable guest rooms. It was completely refurbished in 2001 and features an affordable Wi-Fi connection throughout.
Catalani e Madrid Hotel is just a few hundred metres from Loreto metro stop, which both the red and green metro lines pass through. Rho Fiera Exhibition Centre can be reached directly by metro from Loreto.