3" for me... Screw low snow conditions and the possible small loss of performance i'd have with the 3" vs the 2.6. Well worth it when the conditions are what we all dream about and live for... 3 feet + of fresh deep pow. When we get what we all wish for I want to kill it, and have the best chance to go wherever I want, and have the best chance of not wasting my days energy on getting unstuck. I wana blast through areas with the most confidence a sled can give me which in this case it the 3". I'll be happy to run my scratchers etc. and tool around on those non deep snow days. Reality is even in hard pack conditions we all know how to find soft deep snow in the north facing treed areas and would still be glad to have the 3 inch taking us further then the 2.6 will. Personally I've always taken the longest tracks, and most cc offered and been glad with my choice, but to each his own. Chain case or belt drive... who cares when the pows over the hood. Honestly I don't think anyone who didn't know which they had (QD or chain) under the hood in 3+ feet of fresh pow could tell the difference... its WFO all day anyway in 3 feet + which is how it should be, and the belt drive or chain case isn't gonna change the smile on my face. Oh did I say I'll take the 163 with the 3" all year long
Forgot... The question was originally "which is the best all around track?" Well I guess if you care about less then perfect days go with the 2.6 IMHO