caratsoup,
depends. some of my friends hv very steady hands so they find it easy to apply from the start.
for me, i needed some practice, in the sense that in the beginning, i needed more time to apply it nicely and always has a cotton bud and cleansing cream ready on hand to correct mistakes. basically, when you are just beginning to use liquid liners, try to only use it when you have the time. when you are more familiar then you can do it faster.
yes, pencil ones by the end of the day, sometimes your natural face oil or make up touch up can smudge or remove your pencil liner. however, a waterproof liner stays true and the same all day long!
Personally i use both pencil and liquid. pencil for very casual days eg going to market, hawker centres etc... liquid for work, shopping, night and on "sweaty" ocassions eg bbq, zoo etc...
For work/shopping/night etc, i end my liquid liner with a slight curl at the outer corner of my eyes to 'open' up my eyes more, as well as to give it a more dramatic effect, which i think is quite sexy. ;-P
For 'sweaty' events, i do not do the curl at the corner for a less dramatic effect.
however, if i am just going to a friend's place for casual gathering, going to HDB centrals etc, then i will just use pencil liners.