Choose Master/Slave MultiServer VPS

Hi.
I will follow this How-To in order to setup a MultiServer.

I have 2 vps servers.
1xCore CPU 1GB RAM 100GB space 1TB bandwidth.
2xCores CPU 2GB RAM 400GB space and 4TB bandwidth.

I will also add own nameservers and install java 1.7 and tomcat 7 to deploy web apps.
It will be used for deploying and running small java applications(with MySQL connections).
Secondary as mail and name server.

Well any ideas how to choose which one should be the master and which one should be the slave?

Thank you.

 

I see.

EDIT: Actually both are going to be nameservers. I will use the 1 core as first nameserver as you recommended.
Thank you.