c++ - Which algorithm brings the best performance?

I have a piece of code that is really dirty.

I want to optimize it a little bit. Does it makes any difference when I take one of the following structures or are they identical with the point of view to performance in c++ ?

for(unsigned int i = 1; i < entity.size(); ++i) begin

if
 if ... else ...
for end

for(unsigned int i = 1; i < entity.size(); ++i) begin
if
 if ... else ...
for end

for(unsigned int i = 1; i < entity.size(); ++i) begin

if
 if ... else ...
for end
....

or

for(unsigned int i = 1; i < entity.size(); ++i) begin
if

 if ... else ...
if
 if ... else ...
if
 if ... else ...
....
for end

Thanks in Advance!