I make and shoot both.
I think Flemish takes a little more practice to make well, and get the length right...especially if you deal with different materials, but once you get the hang of it one is as easy (or hard?) as the other. Same for the time it takes to make them--not much difference for me.
My personal experience is endless can have a little more noise, especially on recurves--but there's a ton of variables besides endless or Flemish.
I've seen some crazy statements made about strings over the years...tempted to list them, but no need in stirring up stuff. I'll just say none of them could verify what was said and leave it at that. Point being, don't believe everything you read (remember that insurance commercial? Bonjour!), especially when it comes to strings.
Properly made, either one will do the job just fine. Just depends on your preferences...Ford, Dodge, Chevy; blondes, brunettes, redheads; longbow, recurve, selfbow; etc. etc. etc.