First, where do you live? What brands are sold by local retail stores? Only buy a brand that you can have serviced and that provides free "learning" classes. After that, how much do you want to spend. You must compare apples to apples. Why don't you find a good dealer who sells several top brands--Pfaff (my choice), Bernina, Janome, Brother, Viking and get a gift certificate so that your wife can choose. Otherwise, it's like her buying you a car when she's never driven. Would she know how to judge what to get?
Good luck.
SandyQuilter