|Image borrowed from thinkcrafts.com via Google Images|
Now, functionally, they're essentially the same. With straight needles you would typically knit flat (like a scarf), and with circular needles you would knit things like socks and hats. You can't do that with flat needles. Reason numero uno why I prefer circular over straight! Straight needles are fairly limiting.(Learn to knit flat with circular needles here.)
Reason number two? With some circular needles, you can adjust the length of the "string" that connect the two needles which allows for a larger range of products, literally!
Number three: If your circular needles are attached, you will never have to say "Where is that other needle?!"
Now, I should point out that there are double pointed needles. They're used for I-don't-know-what-yet (I will get there when I don't risk poking a baby with the needles, lol!), but if you don't need the double tips, I suggest just going ahead and buying circular. You can knit flat with them without limiting yourself to just flat projects!
May muses whisper to you always,