1 Zubeldia
2 Popovich
3 Mayo
It is possible that riders such as Armstrong, Simoni, Hamilton etc could continue for the next two years, but the list of potential grand tour winners could easily reach 10 particularly if the Vuelta is taken into account which remains the easiest of the three big tours to win and is usually the most open.
Looking at TDF candidates, Popovich needs to raise his game this year and show that he can compete in the Tour (providing his team is selected). There have been many young riders who have done well in the Giro but have failed to translate this into Tour success (Salvodelli,Guerini,Lelli). Although he is the weakest time trialist of the three riders mentioned, I believe that Mayo has the climbing talent and aggression to win big tours whilst the other two have proven to be followers rather than attackers. This strategy may deliver podium places but could fail to achieve the big wins.