You know what they say, ask 10 bee keepers a question and you will get eleven different answers.
so here's my take.
Budleia and Forsythia are useless for honey bees, in fact Forsythia doesn't do much for anything but looks nice. Budleia will only see a honey bee in desperation, great for a handful of butterflies, hover-flies and a some other insects.
If you are stuck in rural France away from plenty of flower gardens then there often isn't much that produces an excess and obviously what there is will depend on your region, all carry their risks and benefits.
OSR (Colza) gives a good spring yield if the weather is good and warm enough, not every bodies ideal taste but gives the bees a rapid spring build up with an excess, needs to be removed fast and spun before it sets.
Tree fruit, apple, pear, cherry, plum etc are all good but risks of cavalier spraying by both producers and "gardeners".
Hazel for early pollen, willows for early pollen and nectar.
Blackthorn as mentioned but probably more interesting to other types of bee, butterfly and insects.
Lime trees are great (pollen and nectar).
Sweet Chestnut yields well, (pollen and nectar), but generally it's a cooking honey for most people due to its bitter taste.
Sunflower I find great and my customers queue up for it.
Bramble is fantastic for honey bees and so many other species as well.
Maize is only good for pollen but for that it is excellent and arrives here in south Vienne at a good time of year.
Ivy is totally magic for taking bees into winter but not for production.
Most wild flowers don't attract honey bees, not to any extent anyway, some of the native herbs are best if you have the right habitat.
Chris