I have a Janome 350e, and love it! I use it a lot more than I expected to, so I'm glad I got a good machine. As for features to look for, I love the thread cutter! Embroidery designs require changing thread often enough that it's a real help that the machine automatically cuts the threads when it is finished with a color. Also, some of the less expensive machines only have the small hoop. I use the larger (5x8") hoop far more often than the small one. The other major feature is that I can use a flash drive to transfer designs from my computer to the machine. Some require actually connecting the machine to the computer, or using other transfer means. I can buy flash drives for under $4, so I have a lot of them (it's better to have fewer designs on the flash drive so you can find your design more quickly).
I know nothing substantive about other machines, so I can't help you there. Good luck!