It's hard to advise you on which framework to choose as that depends more on your requirements than the UI for WPF controls. Basically, you can think of them as the native WPF controls as they're compatible with both frameworks and make the decision based on your other requirements. Additionally, maybe this discussion
on our forums will help.
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Feedback Portal
and vote to affect the priority of the items