The Callao–Plaza de España half is livelier and closer to Malasaña; the Metrópolis end is more elegant and closer to Chueca and Recoletos. Rooms over the avenue itself come with the view and the noise — the same buildings' side-street rooms are quieter and cheaper. Plaza de España's renovated gardens make the western end greener than you'd expect.
Gran Vía lists around 410 bookable hotels and guesthouses, from roughly €48/night. Prices on the area page are live; booking 3–6 weeks out usually lands the best rate, with free cancellation on most rooms.
If it books out or you want to compare: Sol (from €45/night), Malasaña (from €42/night), Chueca (from €46/night) — each with its own area guide on this site.
Curated picks are coming — meanwhile, the live search covers every bookable property at the same price or better.