MX costs for Mail Servers.

[Manjunath H N]

Hi,
 
What is the best method to deploy MX cost on our DNS servers ??
 
Currently we have 3 MX records, two with the same cost(10), each is from
a different ISP in the same geography & another MX record with cost (20)
in a different geographical location. I feel this is a good
configuration.
 
Is it better to have all the three servers with different costs or the
current configuration is pretty robust if not what is the best practice
for such a scenario.
 
TIA
Manjunath H N