When I make meatballs to go into a tomato sauce, I always pan sear them to get a nice dark brown crust on them then put them into the sauce to simmer. After searing all the meatballs, I deglaze the pan with some of the tomato sauce and add it all back into the pot. Can't pass up all that flavor!
I usually make a bunch (3 or more pounds of mixture).
I brown in the frying pan, then transfer to a baking pan and finish in the oven. Makes at least 8 meals, so I vacuum pack and freeze the excess.
I've fried them, baked them and even poached them (as albondigas), and I think that fried is probably the best. Just be sure to start them on medium and gently turn them as they cook so they don't fall apart. Or you'll have a pan full of hamburger....
I have been known to pan fry them then finish in the oven; pan fry then finish in the sauce; or pan fry then finish in the slow cooker in a BBQ/apricot preserve sauce as cocktail meat balls.
I have never done the really large meatballs only the small or medium sized meatballs.