So, what is the difference and which is better?
Primroses generally have single stems each with one flower on top and many of them. Polyanthus have just a few large stems each with a cluster of flowers on top. The picture shows Polyanthus, they tend to flower a little later and are just a little bit more hardy. Primroses are shorter growing than Polyanthus so less suited to growing with tall plants like tulips and wallflowers…use Polyanthus for that. For most purposes I’d say choose Polyanthus unless you can get hold of some old style Primroses like the Irish ones from Fitzgerald Nurseries.