According to the URI standard the path is for hierarchical parameters and the query is for non-hierarchical parameters. Ofc. it can be very subjective what is hierarchical for you.
In situations where multiple URIs are assigned to the same resource I like to put the parameters - necessary for identification - into the path and the parameters - necessary to build the representation - into the query. (For me this way it is easier to route.)
For example:
/users/123 and /users/123?fields="name, age"/users and /users?name="John"&age=30
For map reduce I like to use the following approaches:
/users?name="John"&age=30/users/name:John/age:30
So it is really up to you (and your server side router) how you construct your URIs.
note: Just to mention these parameters are query parameters. So what you are really doing is defining a simple query language. By complex queries (which contain operators like and, or, greater than, etc.) I suggest you to use an already existing query language. The capabilities of URI templates are very limited...
