Frank,
the Ultracam does not hold it's brilliance as well as the Astroflight does, but for my use it does not creep near as much, and that is why I use it.
Performance wise, they are almost identical.
The creep that I get with the Astroflight isn't really a problem, and I recommend it highly for anyone who wants to use it, but for me - I like to keep my strings at a maximum of 3/4 twist per inch after shot in, and I have to build the AF real short, to achieve that. The UC gets me at the twist count I want real quick, and it stays there.
I used to build endless strings all the time, but haven't built one in probably 10 years or more. Personally I think endless is a better performing string, but not by much, and I just like the look of flemish, so that's what I build for myself.