Which type of nylon strings produce the highest output? material , brand etc. Also do u think a higher tension string will produce the highest volume on a medium sized body?

Im going to be busking with some friends and we will use some portable battery amps. I would like to have the highest acoustic output possible so i dont have to drive the little amp.

Higher tension doesn't move as much, so therefore will be lower in volume.
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
I've never heard of such a thing. Please post some charts and graphs n' whatnot...
"Practice doesn't make perfect. Perfect practice makes perfect." -some dude
I've started checking. It appears to be complicated, and varies between heavily and lightly built guitars, for example. I've posted a question in the classical guitar Usenet group, which has some pretty heavy-duty players. The first reply indicated that initial attack was stronger with heavy strings, but decay was faster - I found similar things in the fora. I have one lightly-braced steel string guitar in which heavy string give a loud attack, but "choke" very quickly.

More later.
In the most general terms, higher tension strings will impart more energy to the top. You'll remember from high school physics that in order to increase the tension without increasing the frequency you'll need more mass, and of course energy increases proportionally. So there is more energy there, for fairly straightforward reasons. Generally there is more than enough energy from the pick/finger to move the string, so the string's mass seems to be the largest factor in how much energy it can transfer. It is of course one reason why larger gauges are used for the lower strings, because an increase in amplitude is not nearly as efficient as adding mass in this case. So it's not really correct to say that higher tension strings will have less volume because they don't "move as much." They may choke the top (more on that next paragraph) or be less efficient, but it is not quite as simple as that, and it certainly is not true that they will universally be quieter than analogous lower tension strings. In fact if forced to make a binary statement I'd have to say that more tension will more often generate more volume.

What is not nearly as straightforward is whether that energy will actually result in more volume from the instrument. Mostly what we're concerned with here is the vibration of the top. The mass, dampening, stiffness, etc of the top will all come into play. The extra energy from higher tension strings is sometimes wasted, because the top cannot handle the extra energy for one reason or another. Sometimes it's because the top is too light, and the top is "overloaded' or sometimes the top develops odd canceling vibrations, or just sounds funny because the extra energy shows up at unpleasant harmonic intervals.

So, in the simplest terms, and if the guitar can handle it, higher tension strings should often increase volume. In practice, there are often a lot more variables that make some guitars react differently.
^^^^ The contents of that thread I linked are fairly typical of what I found elsewhere with a google search. That is, it's complicated. If a classical luthier posts anything there, I'll report it.

I've got one lightly braced steel string that "chokes" if I put medium strings on it - a loud "thump", then nothing.
Yes, I think that's fairly consistent with my experience/understanding as well. My knowledge is more in the realm of bowed instruments, but a lot of the concepts carry over. I've talked about this extensively with a few string and instrument makers and "it's complicated" is probably the best short summary.

The "choking" on a lightly braced instrument makes sense to me. The top cannot handle all that energy all at once, so it experiences destructive/interfering vibrations. The energy is still there but it's not effectively translated into sound.

It's useful to visualize tops somewhat like cymbals - a very small cymbal can be plenty loud when used properly, but if you really wallop it, it's going to expend a lot of that energy by swinging wildly around, which is very different than vibrating. The same amount of energy is expended, but less of it actually goes towards vibrating and creating sound. This is consistent with your lightly braced guitar - the top is "flopping" rather than humming along at a nice consistent frequency like it's supposed to. A larger cymbal you can hit really hard and it will still transfer most of that energy into vibrating instead of flopping around, making it more efficient at transferring large energy inputs into sound - same thing with a heavier or stiffer top.