I think it depends on what you want to spend and how much you plan on using it. As has been said, the "homeowner" models are basically worthless. I always see a bunch for sale on Craigslist as people buy them, find they don't work well and then try and dump them. The only one I have seen decent reviews on our the Mackissic
chipper/shreaders. People who like to create mulch piles seem to like them to process the material prior to placing it on the mulch pile. I would not recommend one for any serious chipping.
http://mackissic.com/consumer/csconsumer/chipper_shredder_consumer1.htmMacCis
I picked up a used free standing manual feed Bearcat model 73420 for $1800. It had a 20 HP Honda engine on it and it was rated for 4 inches. Even with the 20 HP a 4 inch log of any great length would stall the
chipper. I had to section them into 3 foot sections to run them through. Smaller branches of any length it would just suck in and chip. I ended up selling it and I now rent a large commercial hydraulic feed unit when I need one.
If your budget is around $2000 as stated than a PTO driven gravity feeding unit is the way to go. If you want hydraulic feed, I would go with a used commercial unit as they can be had for the $4,000 - $5,000 range which is similar $$$ to what a PTO driven
chipper would sell for with the hydraulic feed option.
One benefit of the free standing
chipper is you can bring material to it with the tractor grapple etc. You can also have two people working, one using the free standing
chipper and one using the tractor to bring brush or logs to it. If you have a PTO driven
chipper you are going to need to create the pile you are working from first and than park the tractor and use the
chipper. If you have difficult areas to get a machine into a PTO tractor mounted
chipper wins there to.
Just my 2 cents worth.