Best fishing line?

I plan to replace all the line on all my fresh & sal****er reels.
I'm still using the old open-face spinning & Ambassador baitcasters
for sal****er trout, reds & flounder - as well as bass in fresh water:-)

QUESTION:
Is there one good monofiliment type line that I can use for both
fresh & sal****er?

Here's my order of interest:
1. Will not tangle (curl up) - the grandkids will be using them as well
2. Will stretch - rather than break
3. The diameter of the line should be as small as possible for,
I guess about 15 pound or so line ...
I'm not really sure about the pound rating of the line. I guess
there is some compromise between line diameter & pounds -
but I do not know what that is. "I prefer to give up a few feet in casting
distance & have more line strength - just do not want that trophy to break
the line."

Here's a couple of links that I found.
I was unable to find a really good & objective review of fishing line.

Spider wi
http://www.hunting-fishing-gear.com/...splay/270.html

Fluorocarbon:
http://www.activeangler.com/articles.../invisible.asp

THANKS
Gene