I'm using Salt for years but I don't recommand it. Since time the network coverage dropped and there is limited reach inside buildings :-( I consider changing it so if someone has a good experience with other operators I'm interested to know.

I heard Migros M-Budget is ok and it uses Swisscom network

I'm happy with Aldi Mobile (Sunrise-based)

10.- starter set comes with 20.- credit.

Cumulative starting credit bonuses:
+10.- if you register online before going to get the card in an Aldi store.
+50.- if you are migrating from another provider (prepaid or subscription), or use a referral (contact me ;o) )

Service quality wise Swisscom are still the best, so you could check out their prepaid options and top-up packages depending on your use, especially if you use it as a second line:

https://www.swisscom.ch/en/residential/mobile/subscription-tariffs/top-up-easy-credit.html

They also have inOne plans, which are post-paid but are not very expensive, costing around CHF 14,50 in the first year and then going up to CHF 29 per month, so it all depends on your particular use.

Good luck!

Slava