I prefer to use Sunil's way of writing query when I have optional (can be null) parameters in the procedure. I don't see a logical reason to use CASE, or ISNULL statement.

Sunil example is not anything new. Like anything in live, this too have some good and bad sides. The good ones are that is very logical, easy to debug, don't have a problem of sql injection etc. But also have bad side like the one that it can't use the cached plan for the query. In the other side creating query dinamically as string and executing with sp_executesql have all the bad sides but one good and that is that can use cashed plan. In most of situation we should use the first one, becuase if has more good than bad sides. But it becomes very usefull to use second one when we search very big table with milions of records.