was playing dota 2 the other day and ran into someone with the tag Soju on the other team. But it wasn't you T-T.
dkuo: as far as options after rising uair, it depends a bit on the char I'm playing against. Fast fallers I'll usually just go for more uairs if they seem to be DIing in, nair/bair if they're DIing away (dair would do more, but nair/bair comes out faster so I can keep it ambiguous as to whether I'll nair/bair or uair to not give them time to adjust their DI). Vs most other chars it's a combination of what will actually hit them (on floaties once you can't connect dair after uair anymore, you can just nair before they float out), and then positional advantage if I have multiple options.
Nair generally will give you a better position afterwards, especially if you want to do like rising uair, double jump, nair but start it above the opponent and fastfall into them so the knockback is greatly decreased, then dash towards them to threaten usmash or another aerial (or maybe a techchase on fastfallers). Similarly there was what you were talking about with using platforms to help, since nair has less landing lag than your other options so you can aerial just as you land on a platform and follow up easier.
Also with the starting animation on dair, I'll be a little worried against some chars that have good quick aerials, especially if I have to also spend a little extra time to position dair so that it will hit after the uair. For instance, dair can be kinda risky against say Luigi, because if you give him any time at all between when uair hitstun ends and your aerial connects, you're getting nair'd. So i'll usually play it safe and go with nair/bair finishers, or possibly try to bait out his nair by staying just out of range when he gets out of hitstun, then going for another spaced uair or something.
I'll use fair occasionally when I want them to stay in place for whatever reason, but this is pretty rare. You can sometimes get like, rising uair, double jump slightly backwards, fair through them (as you're moving downwards and slightly backwards), then uair spike afterwards. Or I can rising uair, then dj ff fair onto a platform, and try to usmash/fsmash/something them as they try to jump out or land with an aerial or something. This is similar to the falling nair example earlier, and falling nair is arguably better for this, but I like the possibility of stealing their jump after fair, or just using fair in general.
But I really like dair. If it looks like I can hit with it, I'll almost always follow a rising uair with dair. The knockback is great, which gets the opponent closer to the edge. The damage is decent, which helps because Pikachu doesn't do damage. You can potentially squeeze out a little more damage with other options, but dair is pretty reliable.