First off, I know this is a duplicate, but I believe this is important, so please keep reading!
As stated in https://bugs.mojang.com/browse/MC-45489 , villager spawning is broken and unbalanced. In my experience, entire villages are populated by Clerics and Blacksmiths, with many villages having NO farmer variants present at all! And the only profession that doesn't have an out-of-whack spawn is the Librarian.

Here's how I propose this bug be fixed:
-Cleric only present if church is present _{(more than one Cleric can spawn in the church)}
-Only farmer variants can spawn in large houses
-Both butcher variants spawn in the butcher shop, instead of one butcher and one farmer
-No blacksmiths spawn unless a blacksmith shop is present _{(OR recombine all blacksmith variants into one blacksmith)}
-Farmer variants most likely to spawn in huts instead of blacksmith variants; I like the idea of other blacksmith variants spawning in huts

I didn't intend to sound immature in my suggestions, I just believe that's the best way to go.