Have used Nikon, Leupold, Zeiss, Swaro's and a few others with good results but last year I switched to Leica ER 5 3-15x56 on my 300wm. Never liked the size or weight of the huge bells preferring 44mm or less but the Leica is so clear I'm making myself get used to it. As good or maybe even a touch better than my Swaro's in low light.