Deciding Between Hidden Powers

Ho-oh is a bit of an odd ball in that he's not really outstanding in any category, but sort of alright in a lot of them. As such, I see him more of a generalist with hidden power assisting in that regard.

I have a perfect Ho-oh and somewhat foolishly bought a second charge move on him thinking he was going to an asset in PvP Master League. That didn't pan out, but when he got Hidden Power I tried my luck and managed to get Ice. The combo of that with Fire Blast and Solar Beam makes him pretty versatile, with coverage against 9 types. Additionally, Ice synergies with Fire Blast against Grass Types, and with Solar Beam against Ground. Not that I necessarily recommend you go down this route as it's not exactly cheap - perhaps I'm just making the best of a bit of a bad situation.

In most cases, HP: Fire/Flying are going to be your two best choices simply because they have STAB and synergize well with Ho-Oh's STAB charge moves.
HP: Grass matches with Solar Beam if you want a tanky pseudo Grass attacker.
If you do PvP, HP: Ground/Water could be fun options, as they're likely to deal SE damage against common counters used against Ho-Oh. HP: Dragon/Ice gives you a Ho-Oh that isn't entirely toothless when up against Dragon-types in the Master League.
HP: Psychic and Steel are amongst the least desirable options, as they perform worse than Extrasensory and Steel Wing.