Since moves have changed

Not knowing IVs I'd power up FB/B as an offensive Mon. IS/IB still hits really hard w/ its HP it's still a pain to defeat. I just wouldn't want to power up a Mon w/ a low CP for defensive purposes. I learned by my lesson w/ Bubble/ IP Poliwrath.

People have to stop believing frost breath blizzard is the best offensive moveset for Lapras. Ice shard ice beam is just as good as fb/b on offense and better than fb/b on defense (which is no longer to relevant with the sad nerf lapras got).
Even though ice shard is slower than frost breath and deals slightly less dps, it balances out by generating more energy. I don't know if DPS × EPS is a good tool to measure the effectiveness of a move, but Frost Breath is 11,11 × 8,89=98,77, while ice shard is 10 × 10=100.
Regarding the charge moves, it probably comes down to preference. B deals 130 damage with a shorter cooldown but demands twice as much energy as ice beam which deals a solid 90 damage. Couple this with ice shard which generates energy faster than fb and you got a lapras who is firing non-stop charge moves.
All in all, if you are searching for a defender, keep ice shard ice beam.
If you are looking for an offensive lapras, which probably is more likely the case, you should base your choice on the ivs and levels of your laprases, since both movesets are comparable.

I say save the stardust, farm Swinubs, and power up a high IV Piloswine with PS/Av instead.