Find a dealer you can work with....who offers service, classes and even hand-holding, if you need it.
Buy the highest grade and style that fits into your budget. Buy the one with the largest hoop you can buy, you will outgrow a 4x4 or even a 5x7 hoop. A color screen is nice, and absolutely a USB drive to transfer designs. I never cable my computer to my machine, I am fearful of a virus transferring to my embroidery machine.
I rcently purchased a Baby Lock Aventura to use in my motorhome. I have a Baby Lock Destiny, but she is too big to take on the road. The Aventura has many of the features of the Destiny, and has a 6x10 hoop. Many of the standard feet are interchangeable between the two machines (saves on buying duplicate feet). Fairly lightweight, about 30 pounds.