Hi Dayna,
First, welcome to the Board! I've learned lots hanging out here, and I hope you do too.
I agree with lots of other people's advice - find a machine that feels right, not just one that has the right specs on paper. Test-driving is important. Also, it's handy to buy from a dealer you can get along with, just in case anything goes wrong. I always spend a day or two seeing how I'm treated in various stores, and how the staff treats people around me.
If you're interested in a Janome Horizon, I would suggest looking at Janomes now - that way, your feet and any extras you might buy will likely work if/when you upgrade down the road. The Brother NX-450Q looks pretty comparable to the Janome 3160 or 4120 (except for the Brother having the knee lift, which these two Janomes don't). My mom has the 3160, and it's great. It's only 12 lbs, so easy to carry to class. It has lots of fancy stitches. The motor is super quiet and pleasant-sounding; this makes it fun to sew on. It's also really powerful; I've hemmed a pair of jeans on it, and it had no trouble with 3 layers of flat-felled seams (so, about 9 layers of denim).
I have the 4120, and I love it. It's about the same weight, has even more stitches, and has the numbered buttons like the Brother to choose the stitches. I chose it over the 3160 because it has a lock-stitch button, which I like for FMQ (makes it easier to start/end sewing in the middle of a piece), and... well, because I like to buy stuff one model up from my mom.
I'm competitive that way!
We both went with Janomes because there are lots of dealers, and they're reliable. They're sort of the Toyotas of the sewing machine world. They both have about the same throat space as the Brother you're considering, and come with a quilting kit (walking foot, hopping foot, 1/4 inch foot, extension table, and I think a couple other things). So, pretty comparable to your choice - just wanted to throw out another option.
Good luck with whatever you choose!