And now for the opposing point of view. I got a thread assortment when I got my machine many years ago. I think it was a good decision. I like to do embroideries with subtle shading and many colors. If I were buying thread by the spool, I'd have all pretty colors, but none of that weird taupe that I need to get my design to pop.
If you are planning on doing simple labels, or kids' designs with large blocks of primary colors, then an assortment may not be the best.
I would purchase a single spool of thread that you are considering for your set and make sure that your machine likes it. I have successfully used Thread Art in the past, but it won't work on my girlfriend's machine. Sometimes they have minds of their own!