I thought my pyracantha were the most useful - all year round either berries or flowers or fresh green leaves and the thorns kept the badgers and foxes out of my small garden. Then, for the first time, a thug of a gull found them and took all the berries over two days. I hope it got a stomach ache.
My roses give the most pleasure. The flowering season can be extended by mixing the flowering periods or getting continuous flowering breeds, not the same as repeat flowering. They don't take much looking after, a good feed in March and July - chicken poo pellets are as good as expensive rose feed. Prune in late Autumn if your garden is windy so the roots aren't too damaged, or spring if you are sheltered. You can deadhead when needed, or, as I do, instead of just cutting off the dead flower, cut the stem down to an emerging new growth. Prune as you go!
Roses are very forgiving. My best ones have been bought as half dead sale items at garden centres for next to nothing and nursed back to life. I don't go to expensive and chic garden centres. I have never managed to propagate a rose but I don't have a greenhouse.
Only sweet peas have as good a fragrance and are as beautiful as roses but are much more work. I think most cottage garden plants are a lot of work to look really nice and healthy - more than I want to give.