"I think vertically is not as good because any exposed part of the cutting will be losing moisture, and the deepest part of the cutting would be prone to rot because of staying too wet."
Brent said it all,about vertical planting,in above statement.!
I plant at an angle 45 degree or so,so I do not have to ,set it too deep,and also leave only one bud above ground.
Also planting in ground ,direct,is a good way when one wait till the soil is into the 55F+
That will be in May here in NJ.
Any sooner and they will just sit in there doing nothing,and maybe losing energy ,every past day.