Why Low G tuning?
All tunes on this website unless stated otherwise are GCEA (Low G) tuning.
A lot of the sound of Flamenco music comes from the bass strings and these are obviously missing using the standard Ukulele high G tuning; so to compensate, the Low G tuning is used to give an extra string to help with the transposing of the music from guitar to ukulele.
How to achieve the Low G tuning
Low G strings are available for all sizes of Ukulele, yes even Baritone Ukuleles - check out http://www.myamoeukuleles.com/stringsAccessories.php
The strings you use are a personal choice and I can only give my opinion based on the strings I have used. I have tried as many Low G strings as I can find (I have a tenor ukulele) and the one that I find best for me is the Worth Clear Low G string.
There are a few reasons why I like the Worth string:
The string has a slight slippery feel to it and my thumb/fingers slip off the string quickly which is useful for longer runs. The tone of it has a mellowness and a brightness (I know that sounds contradictory) but depending on the tune being played it can sound light or it can give a more profound sound.
I like the sustain it has, some strings I have tried appeared to cut off the note as soon as the note was played but the Worth string carries the note for a nice length of time.
A good thing about the Worth string is that it is sold as a double length, you just cut it in half and have a spare.