@Raikou re: Raikou (heh ^_^)
Assuming you'll be using Calm Mind/Sub/T-Bolt and then either Shadow Ball or HP Ice, the use of Shadow Ball would sting his abilities a little, but it would have it's advantages.
Claydol whose Electric resistance, STAB EQ and 120 base Sp Def has always been a thorn in Raikou's side, would be hit a damn sight harder (122 with HP Ice, 160 with Shadow Ball). Gengar also takes up to 92% unboosted which is a nice plus. You also get to hit Garchomp/Flygon and Swampert equally hard rather than picking one or the other, but that's a pretty moot point as you need to be able to OHKO all three of them. Finally, T-Bolt/Shadow Ball is resisted by even less Pokemon than BoltBeam, so that's always gonna be a pro.
Ideally you'd be able to hide Shadow Ball anyway. Opponents would be loathed to send a Garchomp in against a Raikou that they have already seen use T-Bolt/Sub/CM as they'll be expecting HP Ice to be the final move. Sometimes the prescence of HP Ice can have a great effect, even if you don't have it, the opponent doesn't know that. Only show it when it's beneficial to you and it could work just as good as HP Ice. If not, you better have a good Garchomp counter who can cover you when 'Chomp jumps in on a T-Bolt.
In Shadow Ball's favour, your HP Ice 61 would fail to OHKO min/min Garchomp, whereas HP Ice 70 would knock the landshark down. Ack.
The main problem is, if the opponent suspects you don't have HP Ice/Grass, you're Dugtrio fodder. Even after a Calm Mind, the lil moles only take a max of 91%. Watch out for that one.
So yeah, it's a toss up. HP Ice/Grass will always be better, but Shadow Ball is also capable. I guess it would depend on the gap between the IV's. I'd rather use Shadow Ball on a "quite impressive" Raikou, then use HP Ice on a "average" Raikou.
I have thought about this a lot in the past, but I just love Raikou (I mean the Pokemon, not you...but you are cute though
).