This is such a loaded question - a feature that one person loves, another one doesn't. Same thing with brand.
I think the best advice first and foremost is as oksewglad said is to ensure it's a reputable dealer who will provide good service.
Second bit - have your list of "must have features" . If you already have one and are replacing it, what are the wants and dislikes of that particular machine. And the final one I like to throw at the dealer - why should I buy this machine vs any other in the store - what makes it special.
I was recently at a dealer's who has the brand of machine I like. I asked what the differences were between my current model, and the newer version of it. The changes/ new features weren't significant enough for me to want to spend my money.