Initially, I found it a lot easier to cast on a lot of stitches over two DPNs held together, distribute them across four stitches, and join.
At least I was somewhat familiar with this procedure from having knit a lot of hats. By comparison, all the freaky cast-on methods for toe-up socks were a real turn off (until I found My Favorite Easiest Toe-Up Cast On - see previous article for details).
I don't mind grafting stitches, and I fancy myself being pretty good at it. No matter which cast-on method you use with toe-up socks, the toe never looks as seamlessly lovely as a nicely grafted toe on a top-down sock.
The biggest advantage to the top-down sock is that you can do a proper heel flap. Many people (and I am one of them) feel that the heel flap is The Right Way To Do It. I have tried a lot of different heel constructions, but only a heel flap fits my big square heel properly. (I have found a way to make a mock heel flap using short rows on a toe-up sock - see previous article for those details as well.)
Since the pattern is usually just on the leg, you can get the complicated stuff out of the way first. Then it's just mindless knitting once you're on the foot. This can be a nice way to finish off each sock quickly.
For all the top-down socks I ever made, I never knit the leg long enough. I was always worried about running out of yarn at the end, and willing to cheat on the "Oh sure, that's good enough" measurement before I started the heel flap. With a toe-up sock, you don't worry about running out of yarn, and I find it easier to force myself to just knit until all the yarn is gone, no matter how long that may end up being.
Although I am one of those sick and perverted fans of Kitchener grafting, I know that many people are not. Several of my sock-knitting friends always knit top-down specifically because they hate grafting that much. (On the other hand, if you lack experience with grafting, the toe of a sock (which will forever be crammed deep inside a shoe where no one can see it) is a great way to learn.)
Getting all those stitches onto the needles and knitting the first few rounds can be nerve-wracking for the inexperienced knitter. Particularly if you are not very accomplished with DPNs! (Obviously there are a lot of other methods you can use, but I staunchly remain a DPN supporter.)
Until you have knit the first inch or so, the DPNs are clattery and twisty and floppy and absolutely maddening. Once you get that little bit of ribbing on there it stabilizes the needles, so you just need a bit of persistence to get through this stage.
Photo credit: Flickr/prettyglow