I guess I have to switch to wingo/swisscom at some point
Our experiences have always been positive, very few issues, on the train, in the car, on vacation in the mountains, at home (around Aarau), at our offices (Bern and Zürich), and when on vacation around Europe.
My only complaint is that they do that annoying "for the first two years you get a special price!" thing. Just give me a reasonable price and don't bother me with stupid loss-leaders.
Coop mobile has entry-level plans even their “premiums” are not the best because they only rent swisscom’s network. Check their contracts, there must be some speed limitation after a certain amount of data used.
Some comparison websites sometimes indicate the speed limit and data quota for “unlimited” plans. Check https://en.comparis.ch/telecom/mobile/default or maybe https://suisso-romand.ch/en/mobile-plan-comparator/ .
If you want the Swisscom’s network with no real downside you should go for Wingo, it’s owned by Swisscom.
I am not happy. In general, coverage is better than Digitalrepublic (Sunrise). But the actual connection is way worse. The annoying thing is that packet losses are very adhoc, and very frequent. Eg. I open a web page. Page loads fine, images load fine. I navigate to a link, page does not load. Reload, page does not load. Back to the previous page, open the same link, page loads, half the images don't load. etc. This kind of thing happens not just at a train station (lots of traffic), but while stting at home (nobody else around).
By far the most annoying part is when I try to send a message in Threema. In many cases I just get an upwards arrow (meaning the message cannot be sent). It is stuck in that state, so I have to force stop and restart the app, and voila - the message is now sent immediately... This never happened with DR, nor with my previous abos in other countries (ok, I did not use Threema then, but used other messaging apps).
Oh, and roaming, when I go across the border, I have to force-restart the mobile data connection, otherwise it is just stuck and won't work. In comparison my other SIM from abroad happily comes and goes.
I am now wondering if the swiss mobile networks are this sh_t, or maybe my handy is too old and somehow not compatible (it's a OnePlus 5T, I bought it 6 years ago)... and what other provider I should try, maybe raw Swisscom would work better, but it costs more, and requires a 2 year commitment. Which is great if it turns out to be just as bad...
The network issues you're describing sounds like poor QoS class of your traffic. Try to use as little simultaneous connections as possible. If you (your OS) open too many sockets in parallel some of them will be stalled, where the network stack will wait long seconds before reporting any error so the app could re-try. I had this issue with Salt, when doing cloud uploads, S3 or GCP, I had to avoid using the parallel/multi-threaded option of the cmd utils as then the uploads where getting stuck. I confirmed poking with python and Wireshark, that up to 7 simultaneous streems were able to get through my Hotspot from Salt network.