Be sure to use the right kiln schedule, too!
I’ve used both…I did find that with dichroic (the super sparkly coated glass), the Spectrum is smoother, and works well for some jewelry designs where I etched a design and wanted it to be precise. However, I use Bullseye glass almost exclusively. The selection of colors is nice, they seem to do a lot of research and development. I would say that find your local shop, look at pricing on “like” colors (maybe pick a black and compare prices). Some colors are much more expensive, so you can’t look at a piece of black glass at one place and pick a gorgeous purple at the other place….those gorgeous purples will generally be much more expensive.
And BE CAREFUL not to mix them. Nothing is more heartbreaking than creating a design, only to have it crack later because you mixed 90 and 96 COE.
Another suggestion…find a good local studio, or road trip to Austin and take a class from Helios Glass. Their boot camps are amazing. I learned a great deal from them!