Imo the lobster is the best. It's not because of functions etc, but because of it's portability and weight. I've had the tennis tutor plus, spinfire, lobster and silent partner. The lobster you can use the heavy duty battery or use a smaller battery (for weight reasons) now saving 5lbs doesn't seem like much but lifting in and out of the car, up the curb back in out of the car, along with the tennis ball hopper full of balls and racket bag gets annoying.
I think all ball machine owners can agree the biggest hassle to practicing it getting everything in out of the car and back in the car. The tutor player plus is too boxy, small wheels have to bend down to hold the handle. The spinfire was very heavy imo and wider. the silent partner was ok but a little boxy, as the Lobster can fit in my trunk no problem with the handle folded.
Also the batteries are very easy to get to on the Lobster, I put in a smaller battery and my lobster only weights 35lbs. but I have the fast charger and the AC charger.