Peter Sagan
Far and above everybody else. I have been a die-hard fan since Paris-Nice, 2010, and already at that time, I figured he could be the best I've ever seen. And I think it is a testament to the forgetfulness of some people that they say that Gaviria is a bigger talent than Sagan was. Maybe those people should rewatch his two stage wins of that race and remind themselves that he was two and a half years younger than Gaviria is now. Such precociousness and versatility is unheard of and how he has evolved as a rider is incredible. And don't come with your "Gaviria is a different type, and the two are uncomparable"-arguments, because of course that's true. Gaviria is more of a sprinter and should this be winning more than Sagan. He has 14 career wins (on the road - some track exploits should of course be added to that). How many did Sagan have at his age? 36.
Additionally, I am always baffled when I hear people speak of him as a rider whose performances depend on his mood (maybe it is just Danish commentators who say that), given that he always animates any race (away from the high mountains) he is a part of - if he doesn't wait for the sprint in which he will participate.
His off-the-bike-antics are not something I am especially fond of and I find it annoying how he conducts himself in interviews but all is forgiven when he gets on the bike.
Alejandro Valverde
A just as clear number two. As many others, I became a fan when he beat Lance Armstrong in Courchevel, and I am still frustrated by his injury the year after that prevented him from his best ever shot at winning the Tour.
His consistency, longevity and elegance are second to none and I find it upsetting that he has to spend so much of his prime (admittedly, a very long-lasting one at that) helping Quintana. I really hope he can get that rainbow jersey next year.
Esteban Chaves
Personality-wise, he is probably the most inspiring person I have ever seen. His constant radiation of happiness is amazing to behold and it just makes him impossible to dislike.
The Danish lot
Patriotism is difficult to ignore, and in these years it is very exciting to be a Danish cycling fan with so many great talents emerging on the biggest scene. Especially considering the dearth of high-performing Danes since the 1990's (only Michael Rasmussen and to a lesser extent Jakob Fuglsang and Matti Breschel have been lights in the darkness in the meantime). But with Michael Valgren, Magnus Cort, Søren Kragh, Mads Würtz, Lasse Norman and Mads Pedersen, to name but a few, coming up, the future is looking good.
Alberto Contador
To win six Grand Tours after seven participations is pretty incredible. Unfortunately, the ratio is diminishing rapidly, but with his aggressive mindset, he is always guaranteeing an entertaining race. He really should stop spending his team unnecessarily early and often, though, and fewer crashes would also be preferable - although that is probably out of his control.
Ion Izagirre
A very underrated rider (maybe not on this forum but in general). He has found his niche with the one-week races, and with good climbing skills and excellent time trial and descending skills he is quite a complete rider that is just knocking on the door for his first big win.
Imanol Erviti
His two top tens in the cobbled monuments last year was one of the highlights of the spring for me. He must be one of the best helpers in the pro peloton and to see him get his own chances and utilize them so well was really nice to see. Yesterday, he even took a lot of turns on the front on the stage in Paris-Nice even though he had no teammates in his group. Something tells me he is preparing for a repeat of last year's successes.
Tom Dumoulin
He seems like a very intelligent man and his trying to transform himself into a Grand Tour-rider is interesting to watch (if you can even call a rider who has almost won the Vuelta a non-Grand Tour-rider).
Tiesj Benoot
Like Sagan, a very precocious rider. Indrecibly, he is yet to win a professional bike race, but his talent should see him become a big classics contender - maybe already this year. His studying of economics while being a professional cyclist is nice too.
Honorable mentions to Miguel Ángel López, Greg van Avermaet (I know, from a Sagan fan, how dare I?), Michal Kwiatkowski, Primoz Roglic, Michael Woods and Rui Costa.