I think to an extent it depends on what kinds of things you want to make.
Many of my friends who do both tend to knit when they want to make garments - sweaters, tops etc... because there are a lot more trendy patterns for knitting. But for scarves and afghans and decorative items, crocheting is so much faster and I think allows for a bit more creativity.
I can't get the hang of crochet, but I'm a good knitter. I'm also a leftie, and I think that has something to do with me not being able to wrap my head around crocheting (I was trying to learn from my rightie MIL).