I don't know about the best buy for the buck, but I've been using a foxpro spitfire for a few years and it's been exceptional! I use a free program called audacity, download a bunch of sounds from the net, and the create strings to be used... So that I just send one track to the unit, but it has an entire stand sequence already in that one file. I fire it up... And wait for the mutts to come in. Generally, my best string is cottontail, silence, jack rabbit, silence, lightning jack, silence, yote locator+challenge, silence, pup distress, silence, lightening jack2... End. I name them by how long they are. The one I just mentioned is 16 minutes. The I have a 21 minute, 22 minute, and a 45 minute for cats.
I generally keep track of which strings I used last at a stand, and then use a different string on subsequent visits to that stand. I'm pleased with the unit... Just wish it was 100% waterproof. Great for the money though.