please which linux distros is recommended to build router?

I am contemplating Untangle or PFsense.

ENPAQ - features

hardware redundancy support
data backup(data de-duplication)
Voice over IP
Windows Primary domain controller
wifi hotspot
ftp server
mailserver
It inventory management
VRRP support - high availability
monitoring and reporting
Administration-remote, SNTP support
traffic managemet - incoming load ballancing
user authentication and access control
VPN
unified threat managment
firewall
networking- NAT,VLAN,VIRTUAL IP ETC
Derisking access

i will combine Untangle with PFsense, i think that will be cool.

You are best to run untangle in transparent mode behind pfsense.

you will get the hardened firewall with the pf scrub in pfsense.

You can add packages through simple to use package installer in the pfsense gui.