IPv6 internal network is simpler and probably a good idea for a brand-new network.
The big advantage is that don't have to worry about subnet size. No deciding how big subnet is going to be, and either making it too small and having to resize or making it too big and wasting space.
IPv6 is more complicated in that supports multiple addresses, but that is an advantage. For internal use, assign ULA addresses and route those over VPNs. For accessing Internet, computers use the ISP assigned addresses. Then assign fixed addresses from hosting provider to load balancers and external servers. This means that only Internet only sees random addresses; they know the provider but that is known with IPv4.
You ever ran out of ipv4 addresses on a home network? I find this probably does not apply to vast majority of users. And even if you do run out... If using DHCP is it trivial to change network prefix.
(Obligatory "anecdotal, but") I noticed that some routers have a very limited DHCP server, for example being limited to 100 simultaneously-connected devices only. Multi-tenant households with IoT devices may approach that number, the highest number I've seen is around 80 currently.
The S in IoT stands for security, of course. But it's going to be a bummer if my IoT devices forces me or my guests out of my network.
IPv6 can be made stateless with SLAAC so DHCP (and any DHCP-related limitations in the router) are completely out of the picture.
The big advantage is that don't have to worry about subnet size. No deciding how big subnet is going to be, and either making it too small and having to resize or making it too big and wasting space.
IPv6 is more complicated in that supports multiple addresses, but that is an advantage. For internal use, assign ULA addresses and route those over VPNs. For accessing Internet, computers use the ISP assigned addresses. Then assign fixed addresses from hosting provider to load balancers and external servers. This means that only Internet only sees random addresses; they know the provider but that is known with IPv4.