Okay, we're looking at the decision points that go into choosing or creating a sock pattern, and the first one we're going to look at is which direction the socks will be knit in. There are basically two* choices here: starting at the toe and working up, or starting at the cuff and working down. Each has certain aspects that might make it more attractive for given preferences or needs, so we'll look at those.
First, some stitch patterns have a distinct directionality, and that might influence the direction you want to work in. Embossed leaves, for instance, pretty much have to be worked from the base to the tip of the leaf, which means that if you want leaves pointing up, you're probably going to work from the toe, and if you want them cascading down, you'll be working from the cuff. For a turned-down cuff, keep in mind that turning it over reverses the directionality -- cascading leaves on a turned-down cuff would be worked from the toe, and also on the inside of the tube.
Since only one end of the sock is open, you'll have either a bind-off or a cast-on edge, but not both; in either case, these need to be stretchy, so the sock doesn't bind on the leg. If you have a strong preference for which you'd rather do, that may influence your decision.
Although it doesn't have an actual bound-off edge, one does need to close the toe of a cuff-down sock somehow. Some of the more popular methods for doing this involve grafting, also known as kitchener stitch, and kitchener is one of those things that gives some knitters cold sweats. We'll talk a little more, when we get to talking about toes, about desensitizing yourself to this particular phobia, but for now I'll just mention that this could be a consideration. It's not dispositive, though; even if you can't get used to grafting, there are cuff-down toes that don't require it. On the positive side of cuff-down toes, they're much easier to pull out and replace; if you're hard on your sock toes, or if you're knitting for someone who might outgrow their socks before they wear them out, this may be important to you.
Likewise, one needs to get a toe-up sock started. There are a number of methods for doing this, depending on the type of toe one is going to do, and although we're not going to talk about the toes themselves quite yet, we can still look at how this might influence the choice of direction. Some toes start with a provisional cast-on, so that live stitches can be picked up; if you don't like doing this, you might want to work the other way, or at least pick a different toe. Similarly, many of the toe-up toes require considerable increasing, so if you don't like increasing, that might be a consideration. Conversely, if you find getting started on DPNs a chore, but like working on them once you get going, toe-up might be just the ticket, since you can do a short-rowed toe on two needles and only switch to knitting in the round when the toe is completed, which gives you plenty of fabric to stabilize the needles.
Like the choice of toe, the choice of heel can influence the direction you want to knit in. While short-row heels and afterthought heels can be worked with similar ease in either direction, the same is not really true of flap-and-gusset heels. Yes, flap-and-gusset heels can be worked toe-up; however, they're a little on the contrived side, and patterns for them tend to be few and far between, and marked by a definite flavor of how-clever-am-I on the part of the pattern author. So while they can be done that way, they usually aren't; if you want a flap-and-gusset heel, you'll usually be looking at a cuff-down sock. In addition, I alluded previously to how your feelings about increasing might influence your toe consideration; a toe-up flap-and-gusset heel also involves a great deal of increasing, while a cuff-down flap-and-gusset involves a fair amount of decreasing (as do most cuff-down toes, for that matter). If you have particular preferences for or aversions to either increasing or decreasing, that might be a factor in your decision.
Some fans of toe-up socks will cite the ability to try them on as you go as a factor. I actually think this isn't one, as cuff-down socks can also be tried on while in-progress. Although you do have to work the needles past your heel if you haven't gotten to the heel turn yet, you should be able to do so; if you can't, you may have issues with getting the completed sock over your heel as well. In addition, some fans of toe-up socks will do "gaugeless" socks, where they start with one of the increasing toes, increase till it fits, and then knit even except for a short-row heel. This works just fine, as long as you're doing a plain stockinette sock; if you're knitting a self-patterning yarn and want to let it do all the work, this may indeed be a method that appeals. If you're knitting any sort of more complex pattern, however, you're going to want a specific number of stitches, and that makes this method less than ideal. My advice is to suck it up and make the gauge swatch, regardless of the direction you're knitting, and not let this dictate your decision.
Finally, another factor that might go into your decision is how much yarn you have. One very definite advantage to toe-up socks is that you need not decide in advance how long your leg portion will be, but can simply keep going until you run out of yarn or decide you're done. This can be a real benefit if you're not sure you have enough yarn to knit the legs as long as you'd like, or if you simply want to make the longest socks possible for what you do have, and it's not something cuff-down socks can really match. If you're short on yarn, that can be a really strong pointer in this direction.
*Okay, I lied. There aren't actually two choices for direction, but three, because you can start in the middle! Or actually, four, because you could work in from both ends, too, and graft in the middle, but I'm not really sure why you would. Starting in the middle, however, can have some definite advantages. I recently knit a pair of socks where the different factors split pretty evenly. They were for a growing boy, so the idea of being able to rip and re-knit the toes as his feet grew was appealing. On the other hand, he wanted really long socks, so being able to knit them until the yarn ran out sounded good. Starting in the middle was a perfect solution; I began with a provisional cast-on just short of the toe decreases, and knitted the cuff-down style of toe, and then picked up the stitches and knitted upward to the cuff. The result was knee-length socks with an easily replaceable toe, and just enough yarn left to do that -- just what I wanted.