If your user community is rather small and still not so engaged, you should better avoid complex Twitter contest mechanisms that require a lot of engagement from contestants. This way, your Follow&RT
will be equally privileged. For more engaged communities, you can also ask people to generate content, such as in a Picture contest
, or an additional action following participation (become follower / retweet / tweet), even filling in a short mobile compatible form with their contact information to double their chance of winning!