I like the needle threader on my Pfaff 7510. I don't like the one on my Viking Quilt Designer - it gets bent too easily and is hard to use.
I also like the auto thread cutter on newer machines. Love the IDT on my Pfaff. My Pfaff is older so I don't have a start/stop button on it.
My Viking lets me wind a bobbin without taking the thread out of the needle.
Both have "needle down" button - you press it and every time you stop the needle stays down - can't imagine sewing without that.
Also look at the cost of extra feet. Which feet does it come with? Feet for the Viking get pricey.
You may also want a straight stitch plate for piecing.