Hi Jan -
Like machine needles, you need to match your thread to what you're doing. For general sewing (bags, clothes, piecing), I'm happy with Gutermann general purpose thread. I've been using it for decades with very good results and I get it from Joann's. It's a polyester thread and stands up to a lot. If I were hand sewing a chalk bag, I might use the Gutermann or I might look for a carpet thread, which is much heavier and stronger. It really depends on what the repair is like.
For piecing, as I said I like the Gutermann. I also like cotton threads like Superior's Masterpiece and Connecting Threads cotton thread. These are both available online if you are into that at all.
For quilting, I use all kinds of threads, depending on the effect I want. My go-to quilting thread is FilTec's Glide. It's a 40wt polyester thread and quilts like butter. I've never had problems with tension or breakage with this thread, no matter how lazy I am about my settings. I like Superior's threads, but I have to be much more careful about my tension, etc with them. I haven't used the Magnifico much because it's fairly new, but it sounds like it's Superior's answer to Glide so it might be as nice. When doing a tight background fill, I want a thinner thread and generally go to a 100wt silk like FilTec's Allure, Superior's Kimono or YLI's 100wt silk (I don't think it has a special name). I've found all 3 of these threads to handle the rigors of quilting very well and I just pick which to use based on the colors since all of the colors are different. A lot of people also like Wonderfil's Invisafil for background quilting. This is a very lightweight polyester (I believe) thread. I tried this with my new machine but it just kept breaking no matter what needle/tension combination I tried, so I had to go back to the silk thread for that project.
I could go on and on. There are just so many wonderful threads out there! I suggest you try different threads for the different purposes and see which works best for you. I've used Coates & Clark for some projects with good results, so I wouldn't limit myself if I were you. I avoided Sulky threads for a long time because I'd heard rumors that it was a bad thread, but I saw a lot of quilters using it so I got some of that, too, and have had good results with that, too.
As with all things sewing/quilting, sometimes you're results just depend on the machine/operator combination so get suggestions from others, then try things for yourself and come up with your own favorites.
Good luck!