Totem of undying is much easier to obtain in the game and can be held within your left hand, so you can still fight and obtain items while still wielding it. The Golden Apple on the other hand gives you Absorption, Regeneration, Fire Resistance and Resistance which is really good. But if I had to choose one over the other then the Totem of undying wins.

In terms of pure effect, enchanted golden apples are significantly stronger. But totems are much easier to obtain and can be equipped proactively.

Honestly, if you could get one as easily as the other, they're kind of equal.

I don't do a lot of PVP, but I've always gravitated towards totems in survival. They're pretty much a last minute safety net.