I made a little project to calculate that. It gets the prices for API access and subscriptions, and calculates an average cost per token, for a given rate limit. So the cost is cheaper if you get a higher rate limit (cuz you get more tokens per dollar): https://codeberg.org/mutablecc/calculate-ai-cost

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).