To answer this, I think I need to go into a bit more detail. 3 factors:
Aesthetics
Let's start with Raikou. As I said, the storm cloud cape and the tiger patterns makes this pokemon easy on the eye, but then it's just given heap loads of unneccessary stuff which make the pokemon look crowded. The tail sorta works; it looks completely ridiculous but it is hard imagining Raikou with any other sort of tail. The godknowswhat facce though is very offputting; you have the white thingy, the butterfly nostril hair and the grey thingy. It's probably the best out of the legendary dog trio though in terms of design.
Zapdos is simple, yes, butI have to say that's heavily missed in Pokemon with the onslaught of Gen 5 clusterfucks. There's nothing wrong with the design, but there's nothing special about it either; you have the simple yellow/black colour scheme, the spike-feathered wings and the generic beak.
Winner: Raikou
Competitive
Yet how good are these legendary beasts on the playing field. Raikou is not a great OU mon, but is a huge threat in underused. It is also immense in randbats if equipped with a Calm Mind, as it has great speed. it can also take hits reasonably well on the special side, but a lot less on the physical.
Zapdos can run a plethora of sets but is always best as a defensive wall, due to its great typing. Not only that, but it can hold its own in OU as well as CAP if paired with Voodoom (but this is rarely the case). Zapdos also boasts a higher special attack than Raikou. Weakness to Stealth Rock is bad, but I'm gonna still give this win to
Winner: Zapdos
Nostalgia
So how nostalgic are these two mons for me? This one is relatively easy; I hadn't really encountered a Zapdos when I was younger, or even a pokemon card of it. However, I do distinctly remember a rather awesome pokemon card of Raikou right
here. That was still in the later stages of my pokemon card collecting, but I loved that card to bits. So er
Winner: Raikou
Overall: Raikou!