Thanks, Sharon and I'm impressed with your experience -- 50 years! Here's to many more.
I've seen the name Aurifil quite a bit. I'll pick some up, maybe on eBay. I found a seller of Gutermann remnant spools and her prices are the best I've found. I've never had any trouble with the thread (no flaws that I can tell) and it sews really well. Some of the random spools I've found with machines included another brand I've found to be good: Molnlycke.