It depends on individual preference of network engineer. most companies have reserved some addressing space for /30s; if not , then u must use new range. If you want WAN links to be easy spotted (recognized), use different range , like 10.0.0.0 vs 172.16.0.0.
Very large companies I saw use 10.0.0.0/8 range for data, phones, end-users, etc; so, /30 links for WAN links are usually taken from the very last range within scope of addresses. it is like going backwards. so, in your case, 172.31.255.252/30, 172.31.255.248, 172.31.255.244, 172.31.255.240, etc
I would go with 172.16.0.0 - 172.31.255.255 range /16 for medium to small company.
As long as you are using private ranges, what would be the disadvantage of using 10.x.x.x/30 for WAN links?
My opinion it would be ok and if you got a lot of internal ip addresses in 172.x.x.x/x then using 10.x.x.x/30 would be good to differentiate during cases where troubleshooting needed or trace route were used.
Of course, you can use RFC1918 10.x.x.x/8 range.
Because you use EIGRP routing protocol you can do manual summarization on any router in network. However, choose one subnet and divide them in /30 networks and keep them through design. So you can know that these network will be always your device's links.
But if you have some hierarchical design you can use one network from 172.16.x.x and divide them in /30 networks and associate them to device's links and at the top of hierarchy you can summary in one 172.16.x.x network.
In any way you can play with one or other approach its up to you and you network design.