For me it would have to be, hmm ... well, I have so many favorite perennials, it's almost impossible to choose but here are my favorites in lists of five with list #1 (probably, more than likely) being my very favorites.
List 1:
Echinacea
Gardenia jasminoides
Lantana camara
Pentas lanceolata
Rosa Knock Out
List 2:
Agapanthus africanus (Lily of the Nile)
Hibiscus
Lilium longiflorum (Easter Lily)
Passiflora
Plumbago
List 3:
Caladium
Gerbera jamesonii
Oxalis violacea
Salvia
Tradescantia ohiensis
LOL, I listed them all and then moved them from list to list and back again ... I just cannot decide on which 5 I would grow if I could only have 5!