Blizzard vs Ice Beam on Lapras

IB does more damage, but a single IB takes longer to deliver than a single FB - so more time in the attack from IB, but more damage per 100 energy.

I like IB personally, because it can take 3 IB to take down a big Dnite, more times than I will get a kill with a single Blizzard.
I would say it is personal choice as to which you like.

On paper, Blizzard is superior...in practice, it depends on what is in your gyms.

You answered your own question.

If going in a battle and you know it's gonna be easy, Blizzard.

If going in a battle, and you know/think it's gonna be a challenge, Ice Beam. I use Blizzard when I'm prestiging a lot.

2 charge moves will always be better in closer battles, and likely to be better in PvP.

Great question. It's tough to say which one is better for attacking. I have both with FB and with similar CP levels. I like both but I lean towards IB because it's a two bar move and a little more flexible to manage a battle with. But both are great charge moves. Maybe a coin toss situation

The DPs is lower on Ice Beam, but it can be used more often and deals more damage per energy, which is usually a better way to measure attacks.