Are you talking one day, or longer?
Cochem is a nice little town, we spent a day in the town, then a day cycling along river. Struggling to remember much about Trier apart from cycling along river.
Was surprised the guide didn't dress up when she was on Portillo's program.More than enough to do with the castle
Yes, i think it's worth visiting both too, if time allows.Both worth a visit Graham, the Porta Negro in Trier really is testament to the might of the Roman empire north of the Alps, very impressive.
If you do both follow the Mosel between the two (especially if you like wine).