I've done both routes. My preference is the 2004 route as it is more direct and makes it more likely I'll get a decent rest in Menai/Kings. And to be honest, the 2004 is plenty scenic enough.
The only major difference in roads between the two routes is the scenic has a pleasant diversion via Elan Valley rather than a bash along a (quiet) A road. On a good day, this diversion is very much worth doing. On a bad day, it is very much to be avoided. But you can enter the 2004 and ride the scenic diversion if the mood takes you.
The rest of the route is either identical or the scenic has no significant advantage over the 2004 route.