If you are talking about pure stardom and Fanbase then its Ranbir Kapoor, the opening of Besharam(20cr), Roy(10cr) and Tamaasha(10cr) proved that. It just that after opening his films were not liked so they become flop. Fans can't a film HIT but the general audience is.
Bombay Velvet was exceptional case as before release, it didn't had anything to its favour! It more looked like delay project during its release. some more reasons are Budget was too big, director's audience reach is too small, bad release date etc killed it. Even Jagga Jasoos might show the same fate due to above reasons. but the truth is Ranbir Kapoor still has many more Fans in city multiplexe audience and he is bigger star then Varun Dhawan.
Ranbir has got wide acclaim and appreciation for his performances like Raajneeti, Rockstar and Barfi while Varun Dhawan just has one film Baadlapur. He needs two-three more acclaimed performances to gain huge popularity like Ranbir.
Varun too is going strong film by film as he is consistent giving HITS but a film is HIT or FLOP depend more on content, budget, distributor price, domestic share etc rather then Actor. Varun Dhawan is too smart as he doing low budget films till now(Dilwale was SRK film afterall) unlike Ranbir. that's why A Besharam is flop at 58cr nett business but A Main Tera Hero Is Semi Hit at 50cr. A Roy flop at 40cr nett business but Baadlapur is Semi Hit at 45cr, a Tamasha flop at 70cr nett business but Humpty Sharma Ki Dulhaniya is Hit at 75cr.
But no doubt Varun Dhawan is second biggest star among young generation after Ranbir Kapoor, Ranveer Singh is in third position followed by Shahid Kapoor, Sidharth Malhotra and Arjun Kapoor.