I hate tubifex. Such a hassle to keep clean - and if you don't keep it clean enough fish certainly suffer. I bought some a year back (after not having used it for years) and over the next few days I had several dead fish.
I vastly prefer to
culture whiteworms - they are free, and carry none of the aquatic diseases.
Dried tubifex are probably better, but I find fish just pick - no fish I have ever owned has ever particularly gone for them.