There were certain things I wanted when I went machine shopping: needle up/down, thread cutter, auto needle threader and a larger throat. I should have also gone for an even feed foot.
Be sure the machine has the ability to FMQ and take a ruler foot, if you are interested in that.
An extension table is a must if you aren't planning to have a built in table made for it.
I have the Singer S18 (built by Janome, 6500) and love it. My Mom has a Janome 8900 and I love that one, too.
Test drive a bunch a your dealers and be sure you are comfortable with the dealer and know you are going to get great service from them in the event you need help.
Watson