Definitely learn to do both, they are similar only in that they use yarn, and pattern formats are quite similar but other than that they are like sheep n goats.
I do both. If I want something quick n in a hurry, I'll crochet it. Like a hat or slippers. I've done a couple lace sweaters and baby dresses but I knit for other sweaters for adults and knit sox n mittens n gloves.
It totally depends on how you want your finished items to look like. Crocheting with yarn makes a more rustic article whereas knitting with yarn is more delicate. Then there's the whole color work thing. In crochet there is what is called tapestry crochet. I uses multiple colors of yarn just like knitted colorwork but is more suited for more rugged items like purses and bowls and hats that are shaped.
Knitted colorwork can be used more for apparel. So it is a good thing to learn both. One is not tryin to copy or take the place of the other but they both have their uses that belong to each alone.
There is nothing like a beautiful huge tablecloth with glorious pineapples spilling all over the place.
And there is nothing like a luscious light as air, lace mohair scarf.
I hope that I have made my case for both art forms.