1. My 31T5 is still my all-time favorite of the Naglers, and mates seamlessly when paired with shorter f/l Ethos'.
2. I fondly remember how good the views were in the T4's I had, especially when used in my old C9.25; they came about as close to making me feel like I was looking out into space without any glass in between, which puts the T4's a close second to the 31T5.
3. The T6's I owned (13, 9, 7, 5), while very nice optically and a handy "small" size, I never really warmed up to; and as mentioned above already, had a very tight eye relief with the eye guard making it hard for me to settle in while viewing through.
4. While maybe or maybe not a true "Nagler" for the sake of this thread, my 3-6 Zoom is growing on me more and more, even to the point I'm not using my orthos on planets anymore. Sharp, comfortable to view through, easy to adjust the f/l to match seeing, and just all-around fun to use.