What is the best card count for a Magic the Gathering deck?
Generally you should play a deck of the minimum allowed size,
this helps to increase the decks consisency. The minimum allowed
deck size depends on the format that you will be playing, for
modern, standard, legacey, vintage, and casual it is 60.
EDH/Commander allows a minimum of 100( one commander and 99 in the
library). Limited (decks built while drafting, or sealed) has a
minimum deck size of 40.
For a deck of 60 the baseline number of lands is 24, for a deck
of 100 the base line is 37, and a 40 card decks baseline number of
lands is 17.