Ravelry, a community website for knitters and crocheters, has among its countless wonderful features ways search among and to filter its pattern database. A member can look at patterns rated according to which is "most popular" or which has or is being used for the "most projects" among Ravelry members. Ravelry seems to determine a project's "popularity" according to the total of how many projects, blog posts, forum posts, and comments it has.
I'd say the number of projects a pattern is used for is a better indicator of its real popularity than the amount of buzz there is about it. It's easy to admire a pattern, and to post or comment about it, but the real test of how much you love a pattern is whether you're willing to commit to the time and effort and cost of making it. Ravelry's "most popular" pattern has been used for, as of this writing, 8,047 projects among Ravelry members, while Ravelry's pattern that is most used for projects has 19,986 project pages listed, so you can see there is a divide between the two metrics.
Let's have a look at the current top five most-used knitting patterns on Ravelry.
Clapotis, a scarf pattern, is the knitting pattern that is in the most projects on Ravelry, 19,986 to be exact. I can see why. It is a nice piece. But I think equal weight should be given to the fact that a) it's a Knitty pattern and therefore free, and b) it's quick and easy to knit up, given that it uses an Aran yarn. Most of the most-used patterns on Ravelry are smaller items such as accessories and baby clothes. When one filters the patterns by "most projects", there's only one adult-sized sweater among the 36 items on the first page of results.
This is the second most-used pattern on Ravelry, with 19,241 projects, and it's... a pair of fingerless gloves, entitled Fetching. Well, someone had to be making them, given how often fingerless glove patterns appear in knitting magazines. I must admit they are rather cute, even, well, fetching. They are another Knitty pattern, and a big part of their appeal is that they can be made from a single ball of yarn.
The third most-used pattern, with 18,822 projects, is this Baby Surprise Jacket, which is an Elizabeth Zimmermann design. When I look at the pictures of it, I think I might have guessed who the designer was without being told. Zimmermann could design a piece using nothing but the garter stitch and make it look like a design rather than a beginner project. This is not something I see often.
The fourth-most knitted pattern on Ravelry is this sock pattern, entitled Monkey, with 16,139 projects. I'm not sure I understand why. This is not to say I don't like the pattern, because it is perfectly attractive and well-designed, but I've got another sock pattern among my Ravelry favourites that I like just as well, and it only has 13 projects. Perhaps this sock pattern just got better distribution and publicity. It's appeared in Knit. Sock. Love., appeared on Knitting Daily TV, and is a Knitty pattern. Oh, and it's free, whereas the sock pattern in my favourites is not.
This headband pattern, called Calorimetry, is the fifth-most knitted pattern on Ravelry, with 15,313 projects. At first glance I was going to be rather negative about it, but the more I looked at it, the more good points I saw in it. It's a simple-looking piece, but a lot of care and thought has gone into the design. Unlike pretty much every other headband I've ever seen, it's shaped to cover the top of the head and the ears where warmth is needed, and yet go under a woman's ponytail, bun, or fall of hair. It seems to be reasonably flattering. It is a Knitty pattern and therefore free, and can be made with one ball of yarn. One caveat, though. I'd knit it in a yarn that is varied in colour rather than a solid tone, as that will help hide the shaping, which as you can see from the third picture can look a little rough.