In my experience, Stern warranty support has been terrible. I've fixed my own pcbs before stern could provide replacements. From what I hear, Stern hoards parts for new machines instead of letting them out for replacement parts, so if you get a machine with a defective part, you're likely going to have to wait a long time even if they do have the part on hand.
JJP had OK support when I had a sound card issue. They made me jump through more hoops than I thought necessary, but I ended up getting the part in a reasonable amount of time.