I am not so sure that there is a best machine. Most all the hydroseeding equipment today is made by companies that have been around a long time and they are all pretty good.
Finn is always a good choice. They make a quality piece of equipment but they are pricey. Bowie is actually heavier built but not quite as sophisticated. Some of the smaller mechanical units are not quite as heavily built but priced pretty good. Jet machines also work well and are really easy to use.
I don't think looking for the best machine is always the answer. It is more like buying a pair of shoes and you need a machine that fits you and the jobs you do. If the work you are planning to do is fairly challenging such as erosion control work and revegitation then you need a unit that can handle products like FGM's and BFM's that are hard to use. If your doing residential lawns in areas that are not the hottest in the country most any machine will work for you. If you are in a very hot climate then you need to spray heavier applications so you will not get the coverage those of us in the North get.
Basically hydro seeding systems have one of two types of pumps. Centrifugal and Gear. Finn and all jet agitated units use a centrifugal pump. Gear pumps are more powerful when working with a hose but not as good with a platform gun. Centrifugal pumps are lower maintenance. With a gear pump you need to grease it once or twice a day, and there is a stack of gaskets and as the pump loses power you take them out and probably have to rebuild it every couple of years but they are great pumps that will pump anything through more hose than any other pump will.
The hydraulics on a Finn are nice and if you are working with difficult materials it helps that you can reverse the paddles. A few other machines can do that but most can't.
Paddle machines will handle a little heavier slurry than jet machines and you can load full bales without breaking them up but jet machines are easier for one man to run, are low maintenance, work good and are very affordable.
It's all finding what is right for you. You won't go wrong what ever you buy but look at the size of the jobs, the material you want to spray, how many people are available to operate it. Trying to do a 20 acre job with a small machine takes a lot of time. I have done 17 acres on one job with a 300 gallon jet unit and it wasn't quick (but it was profitable). I don't know that I would want to repair someones front lawn with a 1000 gallon machine either.