I agree with tuesy, you are limited if you only have a 4X4 emb field.
Don't be alarmed like I was at first tho, you will need some software too.
I would get a machine that you can transfer designs by using a USB stick. You won't need extra things such as a magic box and stuff.
I hope I didn't confuse you. Anyway, I have a Bernina 640. I like the Bernina Deco 340 too, it uses a USB but is a bit pricey.