All of your dress socks should be over-the-calf, which means they should come up to the bottom of your knee. Period. This is one of the non-negotiables of style.
There are two reasons behind this rule:
1. Mid-calf socks function poorly because they don't stay up.
2. They also lack style because, when you sit down and cross your legs, some skin may be visible between the top of your socks and the bottoms of your trouser legs. This is one of the cardinal sins of style, like wearing a short-sleeved dress shirt, clip-on suspenders, or suspenders and a belt together. You just don't do it.
Mid-calf dress socks are near the top of my list of Things That Shouldn't Exist. And you would do well to forget that they do. I'll never understand their widespread availability (and presumably popularity), especially since higher-end dress socks, like from Polo Ralph Lauren, that are produced in both mid-calf and over-the-calf lengths usually retail for the same price. So apparently the additional material and labor costs are so miniscule that they don't even warrant a higher price -- and, when they do, it's minimal.
But, if both are available, what's the problem?
The problem is that they're not available for more modest prices, especially not in as wide a selection as mid-calf socks.
As an example, Target carries mid-calf dress socks in a dizzying array of colors and patterns, such as argyles and horizontal stripes, for only about $2.50 per pair. But, last I looked, they don't carry OTC socks at all.
Kohl's is similar, except they carry OTC socks -- but only one brand (Gold Toe) and only in solid black, brown or navy, and for about $21 for a three-pack -- 2-3 times the price per pair of a mid-calf pair, which are available in a wide assortment of colors and patterns.
As far as I know, if you want OTC socks with patterns or in off-colors, you're basically limited to top-quality socks, which means spending around $25-30 per pair.
For a more modest budget, you're likely going to be stuck with solid black, brown, navy and gray if you're lucky. Kohl's and J.C. Penney sell Gold Toe socks in the former three colors for around $21 for a three-pack, and Penney's has frequent sales. Jos. A. Bank sells them for $18 per pair, but they're available in more colors, including tan and gray. Socks seem to be one of the few items at Bank that really sell for the listed price most of the time. But, if you get on their mailing list, they occasionally have them on sale for around $4 a pair.
Even if they're more expensive, and even if they limit you to bland choices, only wear over-the-calf dress socks.