If you're publishing a composite locator to ArcGIS Server 10.1, I understand that this is always copied (regardless of datastore setup). The composite locator is just a pointer, so the copy time should be trivial.
That said, I'd still setup a datastore folder entry for your locator. If the locator is on the Server, great, just reference the folder. If its not, share it as a UNC path and reference that. (though UNC takes a performance hit...thats another story).
[or if its a small bunch of locators, maybe you want to copy them, again thats up to you]
Once you have it started, I'd suggest trying it in ArcMap as thats the easiest to consume (move to REST once you know it works).
Either use the Geocode Addresses tool with the Locator Service as input, or use the Geocode toolbar and point the input locator at your Geocode Service. If this doesnt work, it should give you more information on why it isn't working. If it does work, then move to REST and try there. Just a guess but the REST input might not be correct, thus not getting any good output.
Consider the input address here:
1700 Alondra Blvd, Compton, CA
Let's take a look at the address components that were entered. (In this simple case, an address component is surrounded by spaces or a comma. Cities will certainly have multiple words in them and streets will also have multiple words in them.):
primary_number: 1700
street_predirection: none
street_name: Alondra
street_suffix: Blvd
street_postdirection: none
secondary_number: none
secondary_designator: none
city_name: Compton
state_abbreviation: CA
zipcode: none
plus4_code: none
You definitely don't want to return an address that has fewer address components than the input address.
With that in mind, I would recommend considering both the US_RoofTop response and also the US_Streets response. In this case, the US_Streets response has two comparable responses, one East and one West. There is no way for you to guess which one is preferred. The US_RoofTop respons is a duplicate of the US_Streets respons (based on the output address string) so it can be removed from what you present to the user.
No ZIP Code was input, that means the user is relying on your service to determine the ZIP Code. This is important because if the input had included a ZIP code, either 90220 or 90221, you would have been able to narrow the response down to just one address.
So, in summary, Take the response(s) that have the greatest number of address components as they are most likely be more accurate, consolidate down to just unique responses, and present those back to the user. You have then been as smart as you possibly but still allow your user to clarify when needed.
expertise: I work with addresses all day long as a street genius at SmartyStreets.
Best Answer
Locators/TA_Address_NA_10 (GeocodeServer) = North America (including Canada)
Service Description: This locator enables you to geocode street addresses in North America. The locator is a composite geocoder that supports multiple levels of geocoding. The following levels of geocoding are supported in the USA: street address point, street address, street name, ZIP Code, ZIP+4, and city/state. The following levels of geocoding are supported in Canada: street address point, street address, street name, postal code, and city/province. The locator is based on NAVTEQ 2010 Q4 reference data for North America and is limited to the coverage for the United States and Canada. The locator accepts both single-line and multi-line input addresses. The locator can be used to geocode single addresses, reverse geocode, or batch geocode up to 10 addresses per request. For more information, visit us online. Copyright:© 2011 Esri, NAVTEQ.
http://tasks.arcgisonline.com/ArcGIS/rest/services/Locators/TA_Address_NA_10/GeocodeServer
Locators/TA_Streets_US_10 (GeocodeServer) (USA Only)
Service Description: This locator enables you to geocode street addresses in the United States. The locator is designed to support street address level geocoding only. The locator can be used to geocode single addresses, reverse geocode, or batch geocode up to 10 addresses per request. The locator is based on NAVTEQ 2010 Q4 reference data for the United States. For more information, visit us online. Copyright:© 2011 Esri, NAVTEQ.
http://tasks.arcgisonline.com/ArcGIS/rest/services/Locators/TA_Streets_US_10/GeocodeServer