To fill in the blank for your sentence, you could phrase it as follows:

"Which musical instruments are favored among the ethnic groups?"

If you are looking for specific instruments favored by various ethnic communities, here are some examples:

1. **African Communities**:
- Djembe
- Kora
- Balafon

2. **Native American Communities**:
- Drums (various types)
- Flutes (e.g., Native American flutes)
- Rattles

3. **Indian Communities**:
- Sitar
- Tabla
- Harmonium

4. **Chinese Communities**:
- Erhu
- Pipa
- Guqin

5. **Latin American Communities**:
- Marimba
- Charango
- Guitar

6. **Middle Eastern Communities**:
- Oud
- Darbuka
- Santur

These instruments often play a vital role in traditional music and cultural expressions within these communities.