The majority of people that sing in a congregational setting, do not sing “parts”, i.e., the harmonizing alto, tenor or bass notes. Many contemporary songs don’t even have these unless written for group worship.
The consensus is that worship leaders should aim for songs that are between middle C (C4) and the C above middle C (Tenor C or C5). This range will depend upon the ages of the majority of your group. If you are leading a group of children, you can go a bit higher. If, however, you are leading a group that is predominately 50+, you could go for a range a couple tones lower.
RenewingWorship.com has compiled a list of 175 of the top songs on CCLI with the suggested keys for congregational singing. The list includes both contemporary songs and traditional hymns.
I love what Bob Kauflin says on Worship Matters:
Serving the ChurchBob Kauflin, Finding the Right Key to Sing In
Finally, I have to choose, I want to sing songs in keys that are comfortable for the congregation, not me. Ideally, we haven’t gathered simply to listen to my voice, but to each other’s. I want the energy to come from the congregation, not me. That doesn’t mean I can’t do a solo in a key that works for me. But when we’re singing together, I want to serve the congregation. If I’m more comfortable in a higher range, I can always add harmony or vocal fills in strategic places.
While churches can genuinely worship God with songs that are too high or too low, the right keys can help people express their faith-filled praise in ways that are effective, encouraging, and enjoyable.