Personally, I like crochet for projects requiring a firmer 'fabric' such as potholders, hot pads, placemats, rugs, baskets, tote bags and purses. But also for lace-like trims and more tailored edgings. Really don't use yarn with crochet, prefer beefy threads and string.
I like knitting mostly for wearable items...scarves, gloves, sweaters. This is when I use yarn.
Spend some time on youTube; it's a wealth of demo information, everyone showing their own take on the subject. Plus you may want to check out
http://www.knittingparadise.com/ ...it's just like this board, except it's for knitters and crocheters.