My biggest advice is not only to test drive, ask opinions, read reviews...but also visit the store your buying from and speak to them there. I bought a small janome dc 2010 used when I first started quilting. It was/is such a workhorse that I was sure my next machine would be a Janome. (I hate change. Lol!)
Then on this board I heard about the pfaff qe 4.2. It had a lot of praise on the board, there was a nice YouTube video that really showed off the machine.
So, I went to my 2 lqs and looked over both the janome and the pfaff and asked questions about what came with, what kind of support I would get, and what happened if I got home and I didn't get along with it. (Which was a huge question for me because it was a lot of money to devote to a machine.) It ended up being that question that ended up the deciding factor. One shop, told me when I walked out, that was it. The other shop told me if I got home and didn't love my machine, I could bring it back for a trade in for the full value of the machine.
I ended up going with the machine that I felt was a great machine that came with even better support through the store. And I haven't regretted my decision. Btw, I got the pfaff. It wasn't the machine I thought I'd end up with but I LOVE it!