Game Pass certainly is a larger platform than Playstation Now is by over 7x the number of active subscribers.
On cloud users specifically, the numbers are a bit less clear. The
Sony Investor Relations presentation we saw last month indicated that cloud streaming represented approximately 40% of the total playtime for PS Now users as of 3/2021. It is hard to ascertain the specific number of cloud customers, however. For the purposes of this discussion, let us assume that there are exclusively cloud-only users and download-only users - consequently, we could estimate that there are roughly 1.3 million cloud users of PS Now.* I have not been able to find discrete statistics on cloud users of xCloud beyond the beta for Android - but even then, Xbox was declaring that they had hundreds of thousands of users. That figure has no doubt grown since the formal launch, aswell as the iOS + Desktop beta releases. And considering the sheer size of the Game Pass subscription base (more specifically, the Ultimate subscription base), it is hard to believe that a few million have not even just tried a streaming version of a title through the Game Pass app.
* This is obviously very rough napkin math here - but I think it helps to demonstrate that there is a clear discrepancy in scale of platform and serious interest between the two competitors here.
Regardless, I think access to potential users is the more important criteria here. Xbox Game Pass (and its xCloud capabilities) will soon be accessible across Console, PC, and Mobile (Android & iPhone), of which the latter makes for a noticeably more comprehensive platform than the current suite of PS Now access options.