I'm going to be a name dropper here. I avoid Lion brand yarn because I have trouble with it splitting. Knitpicks' Wool of the Andes is another bear. Best ones I've found for not splitting: Caron One Pound, Red Heart Supersaver, and anything with the Bernat name. I also like Paton's.
One thing beginning knitters may not know is that you can also get garter stitch by purling every row. I know one knitter who does her garter this way.