K-cups are great for a single cup at a time. I've been a Keurig user for years now (since they pulled ahead of 'pod' brewers). Horribly wasteful packaging, so I feel a twinge every time I toss a used one. My office is popular at work because of my Keurig machine. At home I have the cheapest Mr Coffee brand K-cup brewer (one cup water reservoir). I like a medium roast and my favorite is Green Mountain's "Nantucket blend."
I tried the "My K Cup" device you fill with your own coffee but I haven't been able to brew as strong a cup that way, no matter how fine my grind. I believe the reason is the water is not in contact with the beans as long by design. There are other refillable K-cup designs I have not tried yet. It was also a touch messy to clean and if I want to work that hard then I highly recommend ... the Aeropress.
The Aeropress makes wonderful coffee, almost an expresso. I add hot water to make more of an Americano (and get 6-8 liquid ounce total per brew). The process looks more complicated than it is and you can get more efficient at it. You can even rinse the filter paper and reuse it a couple of times. You do, ideally, want to burr-grind fresh roasted beans. I seem to like a fine grind, at the risk of extra bitterness. It also consumes a lot of coffee beans per cup compared to a drip system.
Can you tell I really like coffee!
If you're desperate for a quick single serving, the Starbucks Via brand instant coffee is not too bad. It doesn't have an amazing shelf life though, usually just a few months.