I got a Switch in July 2017. I got a PS4 (the pro version) in July 2019.
First-party is better on Switch. Very few could come up with a compelling argument otherwise. But third-party titles are better on PS4. Not only do you have a lot more AAA games, but you have plenty of smaller scale games and indies as well. I know Switch has a ton of small-scale games and indies, but the PS4 still has a good amount.
I mostly play games offline, but PS Plus is far superior to Nintendo Switch Online. Not to mention the option of PS Now. I've never tried PS Now, but it's a valid option for PS2, PS3, and PS4 games.
And of course PS4 can do a lot more besides gaming. DVD and Blu-ray movies, far more video apps, and even a simple internet browser.
PS4 and PS4 Pro are much better in specs and as a multimedia device. Though admittedly PS3 was a superior multimedia device. And portability for the Switch is a great option, though one I don't often use.
I will admit PS4 has the benefit of almost 7 years on the market. Switch has only been out for about 3.5 years. Maybe my opinion will change, but PS4 is the superior platform to me at the moment.
TL;DR PlayStation 4 is the best.
From my experience, PSNow is only really a valid option for PS4 games. I have a decent enough internet speed, but input lag was still a major issue when streaming. Most PS4 games could be downloaded by this point, so it's a non-issue for those. It's a shame because in terms of classic games, PSNow actually has a lot more to offer than Gamepass, but streaming means it's going to be hit or miss.