Whilst growing up, meat was always on our table at meal times- poultry, beef, lamb, and game. My grandparents from both sides of the water would go daily to their local butcher shop (which nowadays is a rarity). All the produce was sourced from local farms and totally organic. Everything tasted so delicious.
As an apprentice cook and privy to working in some of the best Michelin star restaurants around the world, my mentors always demanded the best for their clients. Grass fed animals, organic produce and seasonal was always at the top of the list. Later on in life (after my mandatory training) I was in charge of several fine dining restaurants. With a blink of an eye and without any kind of hesitancy, I too opted for the best. Grass fed Scotch beef was usually on the Ala Carte menu. My opinion on grass fed and what it means; Simply Wow!
Thanks to my good friend Mr. Google, I was able to do some research on this topic. Calves are born in the spring then drink milk from their mothers, thereafter they are then allowed to roam free and eat grass, shrubs or whatever edible plants they find in their natural habitats. The taste is different and is much leaner; in other words not as fatty. With this in mind remember it can be slightly more expensive, as it takes longer for them to grow and may not be as profitable for the farmers.
I recommend you try both. Bear in mind that on the healthier side I would choose grass fed, as the meat contains high-quality protein and various types of nutrients which are extremely important for our muscle and brains. Also, it takes less energy to grow grass than the feeds that are given to other cattle. In a nut shell, it promotes a healthier environment.