Best practice for Pri and Alt DNS settings for multiple site with ADI

Hi
Just wanted to know the best configuration for DNS Primary and Alternate  DNS settings in DCs in second/third logical site
Set up:
One local Domain, 3 physical sites, 2 Domain controllers in each site (All Domain controllers set as Global Catalogues, & DNS (Active Directory integrated zone))
Active Directory subnetted into 3 logical sites.

Site one:
Server 1       192.168.0.1      DNS Pri   192.168.0.2        Alt DNS  127.0.0.1
Server 2      192.168.0.2      DNS Pri        192.168.0.1       Alt DNS  127.0.0.1

Site two:
Server 1      192.168.1.1      DNS Pri        192.168.1.2  or 192.168.0.1       Alt DNS  127.0.0.1
Server 2      192.168.1.2      DNS Pri   192.168.1.1  or 192.168.0.1    Alt DNS  127.0.0.1

Site three:
Server 1      192.168.2.1      DNS Pri        192.168.2.2  or 192.168.0.1       Alt DNS      127.0.0.1      
Server 2      192.168.2.2      DNS Pri   192.168.2.1  or 192.168.0.1      Alt DNS      127.0.0.1

Question:
For site Two, Would I set the Pri DNS on the first domain controller to site Two's second domain controller, or would I set it to site one's first DC?
Same applies for site Three