Hmm, Both Jobs would be pretty awesome.
In my opinion Mythbusters is much more of a science and technology hands on job. Which can involve so many different thing to do.... Eg playing around in a aircraft scrap yard, throwing a crash test dumby around, shooting guns incuding a .357 magnum!
) or driving a remote controlled police car...
Just So many dam things!
Where as top gears basically about reviewing average family cars to some of the best and quickest cars the world in the world with a bit of humor...
Personally Id go for Mythbusters as its just much more varied and has pretty much the possibility to do anything including test that involve cars.