How to choose between 10 speed vs 12 speed drivetrain on mountain bike. Pros and Cons I'm buying a mountain bike from a company that lets you choose the drivetrain. I am having trouble deciding whether to go for a 1 x 10 speed Deore option (11-42) or a 1 x 12 speed SLX (recently released) (10-51) or GX Eagle Sram (10-50) option.  My budget could stretch to the more expensive 12 speed options. But is it worth it? Can't seem to find a definitive answer and cut through all the marketing. What are the  pros and and cons of 10 speed vs 12 speed drivetrain on mountain bike? 

Some obvious benefits of the 12 speed:


Range


Negatives (correct me if I'm wrong):


Less distance between shifts? 
Alignment very important for smooth shifting.
More expensive.
Quicker to wear out?


Previous drivetrains I have tried:


Traditional mtb 9 speed with triple front ring
1 x 10 and 44 tooth front chainring on my commuter bike
2 x ? on my road bike
GX 11 speed when I demoed the mtb I'm looking at
singlespeed huret flip flop
8 speed XTR. 
fixed gear
mountain bike fixed gear 
7 speed SIS 
7 speed gripshit
Sturmey Archer 3 speed Chopper
It comes down to what you would enjoy more - how you prefer to ride vs cost.

I can't find any durability tests I trust but from my reading the general impression I get is that 10 speeds is no more or less durable than 12.

You have ridden many different drivetrains so you have built up experience that should guide your preference. 2 extra speeds in the shifting range is nice, is it nice enough to justify the cost? Only you can make that call.