Proton is still a for-profit company. However, there is now the non-profit Proton Foundation that is the largest shareholder of the Proton company (not necessarily majority shareholder).
Plus, non-profits are not guaranteed to positive. See OpenAI for example.
Voyager is definitely the most polished and great for those who used Apollo for Reddit. It is also very actively developed. For the Android users who do not mind the iOS aesthetic, Voyager is one of the few Lemmy clients on F-Droid.
Thunder is also a great option. I personally prefer its UX more than Voyager, but it is not quite as polished.