There are many ways to test your top five taglines. The most important thing is that you DO test it. It will be tempting to feel the excitement of your internal process and just skip this step.
While marketing companies produce very sophisticated testing techniques, here is a simple one you can do at no cost.
#1 Create small cards that you will use to record a response from at least 50 people. Use card stock and make a standard size note card. On the note care write, "Possible taglines for ABC Church. Please circle the phrase that is most attractive to you if you were to attend a church:" and list the top five options with no numbers, just bullet points.
#2 Ask each person on your team to get 4-6 responses from people outside of your ministry. Encourage them to ask neighbors or other acquaintances for their input. Remind them that everyone loves being asked for their opinion.
#3 Make sure you get at least 50 responses but don't be afraid to get hundreds. Because this is a very informal process also make sure that the folks recording answers don't represent too limited of an age segment. The main idea of this step is to get SOME outside input rather than relying TOTALLY on internal opinions.
#4 Tally the data and create a ranking of your top five list from the external audience responses.