Its between Contador and Valverde. Contador surely has the bigger wins, the Vuelta and some one week stage races (Tirreno, Pais Vasco). Valverde only won FW, San Sebastian, Roma Maxima. Contador further was second in Algarve, Catalunya and the Dauphiné, while Valverde had a bunch of podiums during the saison (2 LBL, 3 Vuelta, 3 worlds, 2 Lombardia) and was fourth in the tour.
Thus Contador has the bigger wins, although its no too impressive though (a really big win was only the Vuelta, which is the clearly least important GT), while Valverde was more consistant through the whole saison (Contador was consistent too, but clearly less than Valverde). Further Valverde gets his results in stage races AND classics. Its reaally close and I can understand if someone comes to a different conclusion, but for me consistence is more important for a "cyclist of the year", thus I choose Valverde.
Behind these two, there are Kwiatkowski and Gerrans, with similar results (Gerrans won LBL, Down Under, 2×Canada and was 2. in the worlds, and 3. in AGR. Kwiatkowski won the worlds and Strade Bianchi, Algarve, was 3. in LBL and FW, and 2. País Vasco.) Results similar but I give a worlds bonus to Kwia.
Nibali won the most important race but was nearly invisible during the rest of the year. This is to little to be the cyclist of the year, but its enough to be in the top 5.
Thus:
1. Valverde
2. Contador
Gap
3. Kwiatkowski
4. Gerrans
5. Nibali
6-10 (in alphabetical order): Froome, Kristoff, Kittel, D. Martin, Quintana.