anti Tag antibody cross reactivity

[Azam Rahimpour]

Hi
does anybody use different epitope tags for proteins expressed in mammalian cells? I have some questions about this:
 
1. Is it important to add small tags to either C or N terminal of proteins?
 
2. Is it necessary to put an spacer or specific sequence between tag and protein coding region?
 
3. which anti tag (FLAG, His, myc, HA ...) has lower cross reactivity to cellular proteins?
 
thanks in advance