In reply to Bobling:
For me, based on my useage, overall leather, but I do use fabric.
Assuming the boots need to be waterproof, I've found in fabric ones the waterproof liner leaks quickly and from approx 6 mths use for the really light weight and flexible boots. Leather, without lining as more comfortable in warmer conditions, can last several year upwards if maintained regularly.
Fabric lighter, little or no breakin period, generally more flexible at least in upper, and need less maintenance. Leather, costs more, needs to be looked after more, heavier, but to me better value over the life, can be resoled if a good quality boot to start with, and can take on more extreme conditions and abuse. I've used a Scarpa SL (full leather) that was waterproof for 10 yrs, and took loads of abuse including some 20 + trips in the Cuillin. I resoled them and although they were no longer waterproof at that stage they did an further 15 yrs of drier summer use.
Never had a fabric boot that could compete (although I am sure that some of the newer ones maybe far better nowadays).
My fabric boots are generally used for lower level walks even muddy and wet ones, but they will not last long where they maybe subject to scraping, sand, gritty mud, abrasive vegetation, etc, which can get trapped in the fabric (as it's normally the grit etc working its way through that breaks the waterproof liner I believe).