Much like Vicious Mockery, it depends on what kind of penalty you want to give. Frostbite deals the same amount of damage as Mind Sliver, but it provides a disadvantage to the target's weapon attack roll instead. Mind Sliver makes your enemies more likely to fail their saving throws, while Frostbite makes your enemies more likely to fail their weapon attack rolls. I would pick the former, though, as Frostbite only has an effect on weapon attack rolls. If your enemy is not using a weapon, the effect will not be helpful.