I find ash to be better at mitigating shock to the hands, but beech to be more forgiving of accidental overstrikes. And beech is definitely more prone to insect damage and rot. But I do find beech pleasant. I do find it curious that Robinia pseudoacacia (black locust) is fairly plentiful in Europe as an invasive but it doesn't seem to get harvested for tool handle usage and hickory gets imported by many tool companies for handles instead. It's surprising to me that a good hickory alternative is available domestically but it doesn't get used for such.
One of the countries with the highest density of pure or almost pure black locust stands in Europe is Hungary. The native forest trees of the flood planes of the Hungarian Puszta (which actually means "desolate, empty place" in Hungarian) were gone by the late medieval times, and were replaced with san dunes. This created dust bowls, which combined with the periodic huge floods, did not allow for much agriculture besides some semi-nomadic cattle and later sheep herding. In the mid 19th Century the Austro-Hungarian government decided to adress the problem by both regulating the the extremely meandering rivers (the Danube and the Tisza), as well as attempting to fix the soil with trees growing well in sandy soils.
They chose the black locust (
Robinia pseudoacacia), a tree native to the Eastern USA (the Ozarks and the Appalachians). They preferred to plant a cultivar called "ship mast locust, or
Pinnata cultivar", which usually has a single, tall trunk. The imported trees luckily lacked their natural insect predators and fungal parasites, which stunt so many black locust trees in the US. The local insects and fungi were no match for the black locust, so the trees thrived and did the job they were intended to do: fixed the soil, created a more fertile topsoil (the tree is a "nitrogen fixing" legume, its roots harbor nitrogen fixing bacteria"). Once the trees, which were planted to block the prevailing winds, were tall enough, they prevented the wind from carrying away the sand. Also, the air became more humid, so the moving sand dunes and the dust bowl gradually disappeared.
This allowed for planting corn and wheat, and provided the locals with wood for heating and later on for construction (the black locust wood has very high BTU). The people discovered that the wood is very tough and also rot resistant, so it quickly became a favorite for all kind of wooden implements, including tool handles. In Hungary one can find black locust axe handles too.
https://www.agoraweb.hu/szerszamnyelek-akacfabol
http://euronails.hu/index.php?route=product/category&path=69
http://euronails.hu/index.php?route=product/product&path=69&product_id=742
https://www.grube.hu/Szerszamnyel/NORDFOREST-hasitofejsze-nyel-ovalis-szem-p0372316.html
In a couple of generations the tree became considered as a true native species, and many of the locals did not know it was just a recent introduction.
The black locust tree was so much associated with the rural Hungarian landscape, that many folk songs commemorated it as the favorite tree, standing around the parental house.
Since its flowers produce abundant sweet nectar, honey production took off along the large pure stands, and the "acacia honey" became the favorite honey of Hungarians. Until recently, Hungary was the biggest exporter of "acacia honey" in Europe. The honey is has light golden color, and is very delicious without any funky or strong taste. Compared to it, the typical clover and other honeys sold in the US all taste "medicinal".
By the way, black locust is called "acacia" in many European languages, because the leaves resemble those of the true acacia's, and also, some of the cultivars have thorns, like the true acacias.
After the fall of the communism, Hungary started to export large quantities of black locust timber, which is stronger and more rot resistant than oak. The French, Spanish and German timber industries did not like the competition under the new free trade agreements, so they successfully lobbied their respective governments as well as the EU regulatory bodies which the Germans and French control, to pressure the Hungarian government to eradicate the tree from Hungary. They were arguing that black locust is a non-native and invasive species (both of which are true), but interestingly did not want to eradicate the tree from their respective countries. What they forgot to mention is that the tree in most of its areas in Hungary did not compete with native trees, because those were gone for more than half a millennium there, and only moving sand dunes remained.
This political pressure caused an uproar in Hungary, and the government(s) decided to resist the EU pressure.
They declared the tree and the honey to be "Hungarikum", i.e. legally defined and protected entities which are typical and/or of exceptional quality, which are part of or define aspects of the Hungarian tradition, culture and excellence. This legal status exempts the black locust from the legal regulations and threats of the EU.
For now, the black locust is relatively safe in Hungary.


According to a 2004 statistics, black locust is the most common tree species in Hungary, comprising 22.5% of the forested land and 12.5% of the tree mass.
I also have to add, that I have never used tools with black locust handles, so I cannot comment regarding their feel. But I am sure, those handles will resist insect damage much-much more, than the beech ones.
Finally, a little extra for FortyTwoBlades - Hungarian scythe snath made of black locust wood:
https://www.agoraweb.hu/termekek/kaszanyel-2-kaccsos-akac-1247