Enolate Ion formation
Enolate vs hydrate formation


Both the enolate and the hydrate form.

Aldehydes (and ketones) react with water in the presence of acid or base to form hydrates. However, for more aldehydes in aqueous solution (even dilute solution), the hydrate is only a minor component of the mixture (~1%). 

The other 99% of the aldehyde molecules are perfectly able to form the enolate, but only a small number of them do because the difference in pKa between most alpha hydrogens on aldehydes and ketones (~21) and water (15.7). 

So, in actuality most of the aldehyde molecules at any given time are neither enolates nor hydrates. Now, if a reaction should occur to consume enolate, then Le Châtelier will come out and nudge the system to make more enolate.


  "Favored" resonance contibutors


The two resonance contributors $x$ and $y$ are not separate compounds. It is not possible for one structure or another to be "favored", though we often use that language because we can relate to comparing the structures of two distinct compounds, like the cis and trans isomers of an alkene. What we really mean when we say "favored" is that the resonance contributor is more important for describing the structure and behavior of the ion than the other. The true structure of the enolate ion is some linear combination of resonance contributors $x$ and $y$ (as well as some other minor things). Thus, the true structure might be like a weighted average over the contributors with $x$ having higher weight. 

For example:

$$enolate = \frac{2}{3}x + \frac{1}{3}y$$