Juliana:
My first thought is to make a list of the things you want a machine to do for you....ie: needle up/down, needle threader, decorative and utility stitches, thread cutter, easy to thread, drop in bobbin, easy adjustments to change stitch length, additional feet at no extra charge, ability to sew wide variety of fabrics including stretchy fabric like knit t-shirts, and last but not least, do you move your machine around, the weight of the machine will be important if you do. You can get this list by going to websites of major manufacturers and looking at the details for different machines. Then when you have the must have list, look at the different machines to see which has what you want in the price range you want. The Janome Jem has s lot of those features and is in the price range. Check it out. There are a couple of versions out there. BTW, I have the Janome 6600 and the Jem. Love them both!
There is a website: Patternreview.com that also has lots of reviews of machines. Good source for info.
Good luck with your search. I am sure others will be able to add to what to look for in a machine.
Murphy