OK, I promised this in a bash I wrote earlier.  Of all
of the Dark Evolutions, I don't understand why anyone
likes some of them.  I think people finally realized
why Dark Primeape is dippy, but I don't see the point
behind Dark Gyarados either.  Maybe it's just me...

Here are the stats for it and its basic counterpart...

Both
Water types
Evolves from Magikarp (Stage 1)
Resistance to Fighting
Weakness to Grass

Base
100 HP
3 retreat
1st attack: 3 water for 50 damage
2nd attack: 4 water for 40 + 50% paralyze

Rocket
70 HP
2 retreat
Pokemon Power: When it dies, 50% chance of doing 20
for all water energy attached to it
Attack: 3 water for 30 + 50% paralyze

Now, here's why I don't like the dark one, besides the
obvious downer of 30 less HP (high for a rocket
pokemon, but that still doesn't make it good)...

Final Beam is overrated.  Sure, it CAN do damage, but
the thing is, you have to flip for it.  Normally, I
like damaging without an attack, but this effect is
mostly lost because A: he can't use it if he's
afflicted by status, and B: It's no good if he doesn't
have any energy on him.  These are the two things that
keep a pokemon from attacking, so why don't you just
use the old one, that has a 50 attack that requires a
measly 3 energy and no coin flip?

Bringing us to attacks, Dark Gyarados's attack is
similar to Base's second attack.  Technically, Dark's
is just as good as base's because one colored energy
is usually a good tradeoff for 10 less
damage...however, you usually put these guys in a
raindance.  Therefore, the bigger, more expensive
attack is actually the better in this case.  Also, the
Dark Gyarados can do 30 +paralyze for 3 water, while
the base can still use that same three water...to do
50 damage!

Because Gyarados is almost exclusively for Raindance,
the smaller retreat cost isn't too impressive either.
Again, you should easily get the energy to handle it.

So, in conclusion, I would use the Rocket Magikarp to
evolve into the Base Gyarados.

(as an aside, I did an entire comparison with no point
system, and on two pokemon generally used for the same
thing, nonetheless!  Learn from this, people)

Xhad

For any disagreements, it's like I always say, it's
better the entire pojo hear it than just me; I read it
religiously anyway.  If you insist on flaming me
personally, it's cmiller@ossm.edu, but don't think
I'll be merciful in my reply if yours is just a flame
and not a viable reply.