If you had to choose?

[Martin H]

Great choice MH, well-thought-out, as it covers such a diverse variety of the plant spectrum
Top of the class - methinks your choice deserves a [ATTACH=CONFIG]75820[/ATTACH]

Sadly I'd have to hand the star back for failing to read the question properly. Rosacaea is a family and the OP wanted a genus...

[rary]

If I had to choose I think it would be lilies, the colour and perfume from some of them is fantastic, and I read somewhere that the roots of some lilies steeped in brandy is good for relieving arthritic pain of the joints, I have never tried this but can vouch for brandy helping, before I got my knees replaced, after drinking a bottle of brandy I had no pain
But back to your question it would be lilies, but a close second would be dahlias, no perfume but fantastic colours and shapes