First, if you don’t have a direct internet connection, you will need a WiFi+Cellular model of iPad - as these have capability to connect to 4G Cellular networks.
By contrast, WiFi Only models of iPad can only connect to WiFi networks - typically provided by you home broadband / Internet Service Provider (ISP) or public WiFi hotspots.
You can directly compare available models of iPad here:
iPad - Compare Models - Apple
The pinnacle of models, offering most features and highest performance (and prices to match), are the iPad Pro models. At the other end of the scale you will find the entry-level iPad8 - which offers good performance, with fewest features, of the current model range. In between, you have the iPad Air4 - which offers much of the performance of the iPad Pro, but without the advanced features. If you are looking for a small screen, there is the iPad mini5.
All run the current iPadOS14 Operating System. All models are available as WiFi+Cellular, or WiFi Only.
A further differentiator between the Cellular and WiFi Only models are GPS positioning. Built-in GPS is only included with the WiFi+Cellular models.