filter design - Filtering on time or frequency domain?

I'm applying an ideal filter on the frequency domain. My code below:

N=512;
fs=100;
t=0:1/fs:(N-1)/fs;

s1=sin(2*pi*2*t);
s2=0.2*sin(2*pi*20*t);
s=s1+s2;
subplot(321), plot(t,s)

S=fft(s);
w=linspace(0,fs,N);
subplot(322), plot(w,log(abs(S)))

fc=12;

H=zeros(1,N);
H( w<=fc ) = 1;
H( w>=fs-fc ) = 1;
subplot(323), plot(w,abs(H))

SF=H.*S;
subplot(324), plot(w,log(abs(SF))) 

ss = ifft(SF);
subplot(325), plot(t,ss); title('Filtered on freq domain')


h=ifft(H);
ss2=conv(s,h);
subplot(326), plot(t,ss2(N:end)); title('Filtered on time domain')

The results are not the same.

And so my questions are:

1. 
   

   What am I doing wrong?

   
   
   


2. 
   

   Is it better to filter on frequency domain or time-domain or it's the same?

   
   


3. 
   

   Sometimes applying a filter on frequency domain results on a "strange" signal after IFFT. Why?