There's a lot of confounding factors, but in general: Cell network uses very little power when idle, but a lot when transmitting. Wifi on the other hand uses a medium amount of power when idle, and a medium amount when transmitting. (this is really generalized and there have been a lot of recent advancements to optimize power usage of both).

This is why general guidance for years was to use wifi when you are actually using your phone for browsing the internet, taking advantage of wifi's lower power efficiency when in use, but to turn off wifi when your phone is just in your pocket/idle to take advantage of cell network's better idle power efficiency.

However, the above is really only true for urban/suburban areas where you have good signal. If you are in an area with poor signal, your phone will use a lot of battery power via the cell network even when "idle" (because in reality even though your phone is "idle", the cell radio isn't actually idle, it's constantly struggling in the background to maintain the connection through the poor signal).