I have both. The carpet (or groundcaover roses I have are Happy Chappy from Jackson & Perkins. They are 8 years old and show no signs of withering. I live in Chicago, so although this past winter was unusually mild with temperatures averaging in the 30s to 50-ish, they have withstood winters of sub-zero wind chills, with average temperatures in the teens to 30-ish. I planted some Drifts last spring which I purchased at a local garden center. The branches are already greening, but this is due to the mild winter. It was so mild here they didn't go fully dormant until almost Christmas. The plants were beautiful last summer. Plenty of blooms for a first season transplant into a garden, but I don't know how they will withstand normal harsh winter conditions.
I actually planted red Drifts to replace some Knockouts which had grown too large for the space they were in. If the Drifts perform as expected they should reach a mature size of around 2 feet high/3 feet wide. This is very similar to the Happy Chappy (and other groundcover/carpet roses). In other words, I think you'll be ok with either, so let color be your guide. Drifts by Star Roses come in red, white, deep pink, coral, a pale pink called Apricot drift, and a yellowish color called Popcorn drift. Carpets/groundcover are available in the same shades. The Happy Chappy is a combination of all these shades which is why I love them in a garden because they coordinate wth anything and everything.
