Which of these two is better in terms of readability and function?
These aren't completely the same.  The first will return a List&lt;T&gt; and the second will return an IEnumerable&lt;T&gt;.

You would need to make this change in order for these to be equivalent.

var list = (from s in _surveyList
            where s.Date.Equals(selectedDate)
            select s.Joint).ToList();


But to answer your question it really comes down to personal preference.  What do you feel more comfortable with?  What has your team agreed on?  

There are cases where you have to use Method Syntax over Query Syntax.  And there are some cases when one will be more readable then others.  You will have to make that determination yourself.

Check out this question over on Stack Overflow.

https://stackoverflow.com/questions/8037677/linq-query-syntax-vs-method-chains-lambda

That question was ultimately closed as being not constructive (opinion related) as I'm sure this one will be also.