I just personally think that the musicianship is superior. Some may disagree. Funny thing is, the two groups (Indelible Grace/RUF & Red Mountain) share some musicians and songwriters.
My church uses quite a bit of Indelible Grace music. I appreciate the endeavor to use many hymns and hymn themes, but to put them to easily singable music. I can read music and spent years in choirs, but many "Trinity Hymnal" hymns still fill me with the dread of difficult (or ugly) tunes. On the other hand, sometimes newer tunes can be near the line of sing-songy. I would love to see a renaissance of musically trained composers in the Church, so that local churches could compose their own songs fitted to their needs. Updating some Psalms tunes would also make a comeback of Psalm-singing feasible!
I lead worship at my church and I love using the RUF hymns, I too love Red Mountain Music, and am becoming a big fan of Sojourn who recently did alot of lesser known Isaac Watts hymns