mercerized thread

You will find most cotton threads for machine sewing are mercerized, if you look at the reels. Here in the UK, look for Guttermann and Sylco. Also look up Empress Mills (their details are on my Fabric list - hit the URL below!).

In Europe, look for Guttermann and DMC brands.

It's widely available as perle cotton or six-strand thread for embroidery but I haven't seen any other form for years. I think my great-aunt had some old sewing thread that was mercerized but that must have been bought 70 years ago.

As for "better", it's good for hand embroidery. I use rayon for machine embroidery and Gutterman for general purpose sewing.

Sally