There are 3 things that Vettel does for the start of the race:
1. he gets pole (so posts an unbelievably quick lap in Q3 - not easy to do)
2. on race starts, he is rarely overtaken (so he consistently is one of the best starters in F1)
3. he is then able to driver faster than anybody else in the first 2 laps, to such a point where the car behind can no longer activate the DRS.
In order to stop Vettel, another driver will have to out perform Vettel in at least 2 of the 3 points I've listed. And unless the rival driver has a better car, I can't see how anybody in F1 can do this.
IMO Alonso is a better driver, but in outright speed (especially in qualifying and the opening 2 laps), I think Vettel is better. Hamilton is probably the only guy who can do the job (ie. out perform Vettel in 2 of the 3 points, above), but he is likely to have a weaker car.
The only way I see that any driver is going to beat Vettel to this year's title, is if they have a better car. Our only hope is that McLaren deliver.