I've always had 2 dogs all my life and now I have 3.  I love Suzy more than the others because she's mine, the other 2 are my Mum's - they NEVER listen to me, they just come to me for cuddles.  
 
But the other 2 I love equally, although differently.  They have completely different personalities but are equally adorable. 
As previously said, just examine your reasons for wanting another one.  Write up a list of the pros and cons and go from there.  If you're having second thoughts about it don't go through with it until you're sure you want it.  If you go into it half-hearted then you will end up having problems.  
