I describe what I use personally in detail here. In short, I use Proton Mail and Proton Calendar (and Proton Contacts). I do use Proton Drive, but only as a backup.
I also posted an answer to a similar question here. To sum up what I wrote there:
I would recommend you use the best tools for you personally.
More generally, don’t put all your eggs in the same basket.
You should really use the best service for each one of your singular needs, and not use the same one for everything.
While Proton’s (still developing) ecosystem is nice, you should really evaluate Proton Mail, Calendar, Drive, Pass, and VPN as separate products. It’s fine to use them all, if they’re genuinely the best options for you (and they are pretty good).
Using the whole ecosystem is not required, and not really recommended (if it makes sense for your use case to use other products), since you’ll be relying on them for a lot of your stuff.
I also have some disappointments with the Proton suite in particular.