I have the 2500 and it works beautifully for my system. According to Monster Cable, the circuitry should be the same as the 2000, but the 2500 has a remote power on/off facility which was for me, the salient feature when I bought it. When I got the unit, there weren't very many conditioners with remote under about $600, so it was a fairly easy decision given my strapped pocketbook at the time. From what I gather, most of the PC manufacturers now offer lower priced units, but I'm afraid that I don't know very much about them. I'm sure that others will be able to provide some insights here.
Before I picked this unit up, I did read a number of comments about the Monster products on the various consumer review web sites, and most regarded the 2000/2500 generally well for the money. I did run across a few negative things on AudioReview about the 3500, with some speculation that it has too much filtering and was somewhat less nimble at handling transient spikes than the 2000, but the vast majority of posts on it were very positive. It might be worth taking some time to read some of these and see what you think.