From the user’s perspective, range will be the most significant difference between mobile data (cellular) and WiFi. WiFi has a much shorter range than mobile, which can provide your device with connectivity from miles away. WiFi’s range is usually limited to a few dozen meters.
Another differentiating factor is service caps. Most mobile data plans are capped and tend to come with steep overage charges. WiFi usage is usually unlimited or is at least limited by a much higher data cap.
And yet another discriminator is going to be performance. When you sign up for a subscription with your ISP, you’re paying for a specified speed – which the ISP guarantees. So you should know what kind of speed to expect, and you can perform speed tests to make sure you’re getting what you’re paying for.
As for the speeds you should be getting over cellular networks, many factors come into play to influence that. With mobile data, your speeds depend on how far the nearest cellular tower is from you and on the protocol used (3G, LTE, 5G) – each protocol having its own upper limit. Your speeds over cellular networks will also depend on the number of users connected to the same cell tower and competing for bandwidth.