Choosing favorites from all generations and manufacturers and models which I've tried... Oof that is a tough question! 
I'm gonna reply with my current gut feeling and say Antminer S2 and Avalon 841!
I liked the big 19" server case and big cards in S2, it cooled very effectively with not much fan speed/noise. The size of it is also an important memory, I really felt being in the mining biz when I had such a big box in the shelf!
A841 I like it for all the tweaking I've done with it and its tank like structure.
I'm gonna reply with my current gut feeling and say Antminer S2 and Avalon 841!
I liked the big 19" server case and big cards in S2, it cooled very effectively with not much fan speed/noise. The size of it is also an important memory, I really felt being in the mining biz when I had such a big box in the shelf!
A841 I like it for all the tweaking I've done with it and its tank like structure.
A841 were nice good downclock make them quiet.
Spondollies sp10 good down clock and quiet.