Most of the information I give you is when you are Not dealing with Class "A" or "B" properties. I would say if you have "higher end" Class A or B rentals, then New is probably the way to go. If you have properties other than "higher end" such as Class C or D properties, I would suggest purchasing used as long as the price is low enough. For example, I know that I can get a cheap new stove for $350-$400. I do not want to spend any more that $150 on a used stove then. I figure if I can not find a good used appliance for less than half the cost of a new one, then I will buy new. I typically do not purchase the extended warranties, it just hasn't seemed to pay off for me. I almost never purchase used from a store because they seem to be too high to justify. I like to use Craigslist and the Habitat for Humanity "Re-Stores". You can also find some at thrift stores. If I buy new, I use Lowes often, and sometimes Home Depot or Menards if I can find a deal.
If you have any other places for good deals on New or Used appliances, please comment on this post.
When you put in a new or used appliance, you should write down the make, model and serial number and purchase date and put it in your file for that property. Then if a tenant calls you with a problem, you can have all that information before even going to the property. This helps save trips to the hardware store after going to the property.