Feedlots and dairies are often criticized due to the barren environment and unnatural animal feed. In both feedlots and dairies, the lots in which they reside can contain rather large accumulations of their manure, and lack access to pasture. On the positive side, they receive a high-protein diet of sileage and corn (with hay added for fiber), which they prefer to eat above anything else (including grass).
The feedlots and the pastures have advantages and disadvantages to the cattle, so which do they prefer? Based on my personal experience and conversations with others, I believe the following. If you place cattle in the feedlot AND leave a gate open that leads to pasture, they will behave as follows.
The cattle will consume almost all of their food from the feedlot diet, and eat very little grass. The grass they do eat is mainly due to boredome. While they will enter the feedlot for food, they will rest and chew their cud in the pasture, prefering the clean spacious pasture to the dirty feedlot for resting.
In this scenario cattle had access to both the feedlot and the pasture. If they had to choose only one, which would it be? I honestly don't know.