Its kind of like going into your closet and seeing a piece of clothing that doesn't fit right, causes problems or just makes you feel bad to look at it. It takes up space and doesn't add any spark to your wardrobe. You just need to say goodbye to it and pass it on. You then free up space for something that does work for you. Gardens are the same way.
This year I've had a draw the line on a particular plant. I would say the name of the plant, but it was a gift from one of my gardening friends and it just has been trouble in my yard. It may work for someone else, but here it seems to be severely prone to powdery mildew and it reseeds prolifically. It just doesn't make me smile anymore and it needs to go. I've been digging this plant up for days on end and I am so very much looking for a replacement for the area it occupied.
Roses seem to be a plant that people often feel like they can't get to grow right. They love them, but can't get past the black spot, powdery mildew, yellow leaves and poor blooming. The problem is not the gardener is most cases, the problem is the variety of rose they've chosen. Unless you are a rosarian with knowledge on how to prevent these issues, you're best to go with proven cultivars for your area.
In Texas we use the Earth-kind™ Roses list tested and proven by Aggie Horticulture and AgriLife Extension as trustworthy choices.
In the northern U.S., Buck Roses are a line of roses tested over the years by Dr. Griffith Buck of Iowa State University. These would fit the bill for more cold hardy cultivars. A nice .pdf publication here on them.
A common rose that I like that grows many places is the Knock-Out Rose™.