I think it will be the Nintendo Switch and you guys ? 

No specific numbers but it seems pretty obvious the ps5 declines from the ps4 which the switch has a good chance of outselling. So Switch

The two don't seem to directly compete anymore. Nintendo have always been smart enough to expand the industery beyond its limits.

But to answer the question. I think Xbox serieses will do better than Xbox One. Which means smaller market for Ps5, compared to PS4.
It all depends on Nintendo's plan of releasing a new console. It doesn't seem to be anytime soon. So I think the Switch to sell more. But it will be close.

Based on?

XBOX series X will be greater competition to PS5 than what xbone was to PS4 and will take away sales. Switch is unstoppable. PS5 will sell 80-90 million units, while Switch will sell at least 120 million and might go as high as 160 million

more competition and a higher price, obviously not the be all end all but I really dont think ps5 will sell more than the ps4 

The problem with the Switch is the possibility of Nintendo replacing it for a Switch 2 to try and keep some sort of power parity, thus cutting the original's legs short.

Probably Ps5... but life is more than just numbers. We need innovation and variety.

Answering a question like this at this point in time is a completely wild guess. I’d agree with the sentiment that XBox will be a bigger competition to PlayStation next gen than it is now, both because it’s more powerful, has a cheaper option, doesn’t look ugly, and they aren’t making the PR blunders they made with the launch of the XBox One. So I’d guess PS5 won’t match PS4 because XBox will carve out a bigger marketshare. In that case, it seems likely that Switch, which has a shot at beating PS4 in the end, will then also remain ahead of PS5.

Why would they do that when even the original Switch never tried to? It was just slightly more powerful than the Wii U (albeit with an architecture which is much better).

I think it's important for console manufacturers to retain a power gap small enough to remain competitive, for sure, but parity was never a goal of Nintendo to begin with.