Ice attacks are most effective against Grass, Flying, Ground and Dragon
Pokémon.
Ice attacks are weakest against Water and Ice Pokémon. A majority of
the popular Ice Pokémon are Ice/Water (there are no pure Ice Pokémon), so
this double-protection is a concern.
Ice attacks have a more sensible distribution than many other types of
elemental attacks. The fewer the PP, the more damage the attack does. Ice
attacks also have arguably the best side effect in the game.
A Pokémon can be unfrozen by certain items (eg, Ice Heal, Full
Restore), but since items cannot be used in link battles, a frozen Pokémon
is as good as defeated in a link match. It's just a matter of having
enough PP left to finish it off. A frozen Pokémon can be switched away and
a replacement brought out, but if the frozen Pokémon is returned to
battle, it will still be unable to do anything. This makes Ice attacks
particularly powerful, much more so than attacks that immobilize victims
in other ways.
A Pokémon can also be unfrozen by a Fire attack, so be careful with Metronome and remember that it's probably
not a good idea to try to finish off that frozen
Mewtwo with your
Charmander.
Something else to keep in mind is whether or not the "Freeze Clause"
applies to your current battle. In tournament play, it is common to limit
the number of frozen Pokémon on one team at any given time to a single
Pokémon. So, let's say you freeze an opponent's
Gloom solid, and he immediately
switches to a different Pokémon. If you use the same Ice attack and
accidentally freeze the incoming Pokémon, you would be disqualified.
Looking at it from the opposite point of view, it is almost never a
good idea to leave a frozen Pokémon in the battle. If you just let him sit
out there and get beaten on until he faints, the icey nuisance that just
froze your current Pokémon will be free to freeze the next. Whereas, if
you immediately switch out the frozen Pokémon, the incoming Pokémon will
essentially be immune to freezing. It will also leave your new Pokémon
free to Explode or Selfdestruct on the last opponent, with
an unfainted Pokémon as backup.
Note that Pokémon affected by another major Status change (eg,
paralyzed or sleeping Pokémon) cannot be frozen. This does not include
minor status changes like confusion.
Blizzard has the edge in this one, excepting the lower number of PP.
Most kick-ass elemental attacks are pretty unreliable, but Blizzard is
surprisingly accurate for its power. Because of this, in the long run,
Blizzard will actually do more damage than Ice Beam over a large number of
attacks. But individual battles are not the long run, and that one missed
Blizzard could mean the end for your Pokémon. Ice Beam is still a very
good attack, and sticklers for consistency won't lose out that much if
they choose it over Blizzard. But do know that Blizzard is as reliable as
mega-powerful elemental attacks get. Choose wisely.
Note that while it is widely-reported that Blizzard freezes the
victim 30% of the time, it actually only freezes 10% of the time. Yes,
really. OK, test it yourself if you don't believe us!
It's still an extremely powerful attack, though. In fact, Blizzard is
not only a great Ice attack, it is one of the best attacks in the game. It
is a very good TM for Pokémon that have a high Special statistic. It's
very powerful and reasonably accurate, and it has probably the best side
effect available. Nothing brings an enemy closer to defeat than being
frozen. Of course, this advice also applies to Ice Beam, if you are
looking for something more reliable (but less powerful).
Ice Beam does more damage than Ice Punch, but has fewer PP. They are
equally accurate. Ice Punch is not at all a bad attack, and it does have
novelty value, but, given a choice, Ice Beam will do you right more of the
time.
None.