Z.ai does have their own subscription, but I haven't used it because their privacy policy was pretty buns last time I checked.
I burn through my current Google AI pro sub for the week in about 2 and a half days so wanted something extra to add to it, but don’t want to buy any expensive ultra plan. Flash models have got me about 98% of what I need, but quotas are still a bit low.
What did you find objectionable? I looked at it when I subscribed almost a year ago and I was fine with it (e.g. they don't train on your API inputs).
"The Company do not store any of the content the Customer or its End Users provide or generate while using our Services. This includes any texts, or other data you input. This information is processed in real-time to provide the Customer and End Users with the API Service and is not saved on our servers."
tl;dr API cost (openrouter) is always more expensive than a subscription (for the same given model). you should always use a subscription first and only go to API pricing if you run out of your subscription.
In terms of which subscription is best, different ones provide different models, different amounts of tokens, different rate limits. So it depends on what model you want and how much you need to use it. The frontier ones are always more expensive than open weight ones, but a few subscriptions are starting to include frontier models like GPT-5.6 Luna (which is a great deal but not necessarily the best price-per-performance).