Which will typically have better running time, multiple if blocks or a single if/else block?
This is largely irrelevant as the semantics are different.
Now, if the goal is comparing the case of
if (a) { .. }
else if (b) { .. }
else { .. }
with
if (a) { return }
if (b) { return }
return
where no statements follow the conditional then they are the same and the compiler (in the case of a language like C) can optimize them equivalently.