what would be the possible approach to go : SQS or SNS?

I am going to make the rails application which integrates the Amazon's cloud services.

• I have explore amazon's SNS service which gives the facility of public subscription which i don't want to do. I want to notify only particular subscriber. For example if I have 5 subscriber in one topic then the notification should be goes to particular subscriber.
• I have also explored amazon's SQS in which i have to write a poller which monitor the queue for message. SQS has also a lock mechanism but the problem is that it is distributed so there would be a chance of getting same message from another copy of queue for process.

I want to know that what would be the possible approach to go.