All I can say is the Delos 17.3mm I have is now my favourite eyepiece.
The only drawback is the large field lens can catch incidental light and cause reflections. The 16mm Nagler is an older design - I reckon the 13mm Nagler is a better eyepiece.
The Delos, in my opinion is the finest eyepiece TeleVue have ever made. They have great contrast, sharpness and colour tone. The field is super flat to the edge and they have a nice comfortable 20mm eye relief.
The 16mm Nagler is also a very good eyepiece, but it doesn't quite reach the optical purity of the Delos. Its main draw back is the 10mm eye relief which some people find too little. I don't wear glasses, but I suspect it wouldn't be an eyepiece for the eye glass wearers.
