Lightning Strike doesn't release bolts, it releases 1 lightning bolt that
arcs from target to target, like a sorc's chain lightning. Lightning fury
releases one bolt for each enemy on screen, and it does it for every enemy
the main javelin hits, which, with pierce and large groups, can be multiple
enemies in 1 throw. For example...let's say you have a clumped mob of 20 or
so enemies(cows for example). You throw 1 LF into the middle of the mob,
which releases 20 bolts, then, the javelin pierces, hits a second cow,
releasing another 20 bolts, then pierces 1 more time, releasing ANOTHER 20
bolts. With 1 throw, you've just released 60 bolts(plus hit 3 cows with the
physical damage of your thrown javelin). Now, when you consider that each of
those released bolts can hit multiple enemies, you'll find you basically
just wiped the entire mob with 1 javelin. Additionally, Lightning Strike's
bolt has next delay, which means after the bolt hits something, there's a
brief period of time(under a second) where it deals NO damage to anything,
but still uses up one of it's allowed hits(this is only an issue if enemies
are bunched up together). To use the above example, you run up to the same
cows to use LS(which puts you in melee range, not always a good place to
be), use LS, you've now hit 1 cow with your physical damage, then released a
bolt that arcs to another cow and hurts it. Now it will arc to another cow,
but because of next delay, this hit will do no damage, then it will arc
again, hurt another cow, arc again but get next delay, etc. So while the
individual bolts from LS are stronger than the bolts from LF, you end up
doing FAR less damage if fighting against a big mob. LS's strength is when
there's only a handful of enemies on screen who aren't all clumped
together(small groups of enemies that scatter like fallen are perfect for
this skill), this way the bolt will arc from one to another without getting
next delay, and without using up nearly as much mana as LF costs(at slvl 20,
LF costs 20 mana and continues going up with each level, LS always costs 9).

Any solidly built javazon will use both skills. For non light immunes, you
should be using LF for big mobs, LS for scattered small mobs, and CS for
bosses, single targets, and small clumped mobs.