The paint we order from Pioneer Athletics. We just use the districts sprayer for our field on a day they're not using it for the game field. They're kind of a pain to maintain so I prefer sharing with them. We can get the whole field done without yard ticks in about a bucket, if we're adding more field marks it can take a bucket and a half. (I think we have 15-15 on our grass field and not quite all the way back to the back sideline for depth)
The spray cans and the little green field striper carts got us by in the past, but I'm not a big fan of them. It costs probably twice as much to do the field, doesn't look as nice, and I usually have a couple bad cans every now and then. Basically you either spend the money on the paint sprayer or the paint ultimately. I also use the districts sprayer when I redo our parking lot with parking lot paint from Sherwin Williams.
Going back to the bigger sprayer is a lot easier to put a string down and make straight lines. The little ones tend to bounce a lot worse on uneven surfaces and it's more of a pain to keep straight lines to me.