way too generic of a question, as
@P4-630 stated fans, heat pipes, how well the tower is built and tower specs all play a role
All above is thru, but with these aspects in mind, the bigger the heat dissipiating surface is (
cooling fins), the more efficient (
not better) a air cooler can function. So, yeah a dual tower has more fin surface to dissipiate heat to the air so in theory it should be more efficient as a single tower cooler (
but only if all other specs are the same).
Regarding the question in the title; for example, the answer is no, a well build single tower cooler can perform better than a poorly build dual tower model.
Best is to know how much heat you want to dissipiate (
which CPU and OC or not) and check the reviews to be able to that cooling capacity than you should be OK.
Depends on how much they cost where you live, what case and other cooling you have and what you're planning to cool. Between those two I'd go for whichever is the cheapest.
As above, this is unique for every situation; available budget, does it fit in your case, noise levels, are the 'looks' are important? and so on.
As long as you just make sure the cooling capacity is suited for what you are going to cool.
It takes some research, but sometimes it's all about the journey, not the destination.
Have fun.