Both types will work, no better than the other. Well made, good quality just like building arrows or such. Endless strings have the advantage of being built in high production, with machines to serve endloops and centerserving. This is why in the late 50's and 60's they became popular. Also the lengths can be more readily duplicated.
Thats about it. Flemish can be made to comparable physical weight, and strength and properly made, no big difference. Also a whole lot of ways to make without a jig, which is good in the field. Also you can't make endless strings with natural materials, sinew, nettle or such ,without a whole other set of processes.
Try both and have fun, that's what it's all about! Good shootin, Steve