I have a 3600 I got at a yard sale several years ago for $5.00
-I don't think the man selling it knew what he had.
I don't know about the other models as this is the only one I have experience with but I really like this one.
The variable speed and reverse are very helpful.
The only thing I would change is to eliminate the faucet (not the right word, but you should know what I'm talking about) on the front.
It gets clogged all the time and is of little if any benefit to me. It's just something that I have to work harder to clean.
I especially don't like it if I'm doing something dry, such as nuts, grain, or bread crumbs as it gets packed full.
But overall I'm extremely happy with it.
-My main use is making carrot/orange juice and it works exceptionally well at this (I do get very small carrot pieces as it isn't a filtered juicer, but I like this and feel it's healthier).
I am my own bad companion