Usually, I think a lot more movesets will have Thunderbolt over Ice Beam. However, I think Ice Beam will be better for your Latios for two main reasons:
1) Ice Beam can counter one of Latios' weakness, Dragon, whereas Thunderbolt does not have any
2) I know you already have Dragon Pulse for Dragon coverage, but that's strictly for Dragon types. Ice can cover 4 types oppose to Electric which can only cover 2. For one of Electric's coverage, Flying, Ice-type works well against - so even if the Pokemon is dual-typed to another type resisting Ice, at least it will deal normal damage. For the water coverage of Electric, it's really just Walrien's evolution line, Cloyster, Lapras, and Dewgong to worry about, so that's 4 out of the entire Ice population. Saying again, you have Ice to counter Grass, Ground, Flying, and Dragon to increase the population of Pokemon you can counter.
Hope I helped! :)