I agree with Midlo Dad, Heavy D & willj1967. If you have a choice, I would go machine pitch. The managers & coaches at the 6 years old to 8 years old level of play in various little leagues across the country are not usually chosen for the BP ability. The machine pitch evens out the disparity between BP pitching abilities in that every player is learning to hit the same basic pitch over and over again. In an issue of timing vs mechanics at this age level, I will take mechanics every time. Timing is something that can be worked on from age 9 on up when they usually face live pitching from their peers.
The uppercut swing coming out of T-Ball is almost always an issue in our league. "Smart coaches" will pitch BP to that tendency instead of trying to break them of it. Machine pitching forces every player to swing closer to a level plane which is more desirable in the long run [although I admit that a lot of major leaguers have made a great living off of an uppercut swing].
I am pretty sure I know what willj is talking about with the catchers. It appears to me that a lot of the critics of machine pitch are assuming that the BP coach pitches are going to be consistently located. In our league that is far from the reality. Therefore, the 7 to 8 year old catcher is constantly [and i mean constantly] missing the ball thrown slightly to his left, or right or [mostly] in the dirt. However, the machine pitch is the same place [basically] every time and the well coached catcher can set up in the same spot and catch the ball and throw it back. Makes for a quicker game and a more confident and less frustrated catching prospect.
Duex ex Machina