I use mainly tens and nines, though i have used strings from 13 set, when i last time broke strings, cause i was too lazy to go to a msic shop and my bro had a spare set of thirteens
loved the thirteens, by the way.
i have a quite low action, i have only my crappy williams acoustic(with a hell of a lot fret buzz ,should fix that)
but then, one day... in school, i got to try a nylon-string (rather cheap quality) acoustic, which had an action so high that i could have put my mobile phone under the string with strings not touching it, and playing with it was just... amazing. loved that.
but high actions not good for me really, cos every once in a while i have problems with using too much pressure pushing the strings.... not good considering the fact that i play piano, plus i sometimes have the notes sounding out of pitch(although rarely, mainly when im nervous, i also often do have a light kinda touch to playing)
wish i could adjust my acoustics action though, would put it super high