I think it's safe to assume that Splash reigns supreme over all other moves stated.
You're just biased towards Blizzard because you like Ice ty--owait.
Trollin' aside, Blizzard really is statistically better than Hydro Pump. Just 'cause Hydro Pump is used more doesn't make it the "better" move. As all competitive battlers know, Offensive Hail is ass 'n always has been, and is therefore Blizzard is rarely used 'n abused due to lack of Hail. There's also the fact that Ice is great offensively (even slightly better than Water, perhaps), but a shit type to have defensively. As a result, there're a lot more viable Pokes that can abuse Hydro Pump than viable Pokes which can abuse Blizzard since while Water might not be better offensively, it's better defensively and in terms of team synergy by a long shot.
Aside from all that, a 10% drop in accuracy (... or was it 15%?) is statistically made up for by the 30% freeze chance. Blizzard is slightly better than Hydro Pump in singles. On the topic of Doubles, damage output and strategic value for two hits Blizzard doles out is much higher than a single Rain-boosted Hydro Pump. Factor in the two chances to freeze, and in Doubles Blizzard is statistically far superior to Hydro Pump.
I still disagree about certain points. For one, Hydro Pump in the rain reaches 180 power (even without STAB), while Blizzard in hail only reaches 120. In the hail it's true that Blizzard has the accuracy benefit. But the fact is that Blizzard is too unreliable to be used outside of hail. The 30% Freeze chance is nice, but Hydro Pump in singles is often the more powerful and reliable choice.
I suppose Blizzard is mostly better in doubles, but you can't say I'm wrong about Hydro Pump having more concentrated power. Spread damage is good, but against an individual target Hydro Pump is much stronger.
Let me review:
+Usable accuracy outside of a weather condition
+More power in doubles/triples and in the rain
-No secondary effect
-Incapable of spread damage in Double/triple battles
-Somewhat inaccurate even in rain
+Spreads out damage in double/triple battles
+Has a good chance to freeze
+Perfect accuracy under Hail
-Nearly unusable accuracy without hail
-Doesn't get a power boost from Hail
-Can't have concentrated damage in doubles/triples
I think we can both agree that Hydro Pump and Blizzard are better then Stone Edge though.
You've just confirmed for me the fact that Blizzard is better, Nick.
When I mentioned statistically better, that's exactly what I meant. Hittin' two targets for a solid 135 Base Power with perfect accuracy in Doubles is much better than a single hit with 185 Base Power. 185 is often either overkill on a strong Poke, or not enough. A ton of power against one target is situationally useful (why the **** won't spell check accept "situationally"? ಠ_ಠ). This is because the need to kill a highly dangerous threat for sure via a high-powered move has nothin' to do with statistics, that is a situational use. I'm talkin' raw numbers, not a possible situation that will arise due to an opponent's team choice. On the other hand, Blizzard is more useful for more situations. Spread damage hittin' for a higher damage total regardless is much less situational in that there's never a chance of overkill; you'll still hit two targets for the price of one move. Factor in a miss from Hydro Pump, and that boost in power meant nothin' during that turn. Blizzard won't miss.
In Doubles, outside of weather, Blizzard is still more useful for the same reasons. 70% accuracy to hit twice, or 85% accuracy to hit once? Odds say the former will hit more times than the latter. Factor in the 30% freeze ratio every hit, and it's obvious which move is better.
In Singles, during the appropriate weather, I couldn't say which one is better since it's not wholly apparent. Blizzard no longer has the obviously superior damage output since there's only one target. The 30% freeze chance and lackin' the risk of missin', while Hydro Pump's occasional miss might make Blizzard statistically better. Unfortunately, I ain't particularly good at crunchin' numbers of chance and such, so I'm not sure which one is better in raw math.
In Singles without weather, Blizzard is clearly better, but very marginally so. -15% accuracy for 30% freeze chance takes the statistical advantage very slightly.