Any Magic Online player will tell you that 8-4 drafts are the place to be if you want the best competition and the most return on your drafts. I'm not here to disagree with this assessment—it's clearly correct. I fancy myself a pretty decent drafter and have won my share of 8-4s, but without fail, I begin each new format jamming Swiss drafts.
I like Swiss drafts early in a format for a few reasons. First, I just want to play as many games as possible. If I lose in the first round, I want a slightly larger sample size to decide whether that was variance or bad strategy (and really, even three matches is not much of a sample size, but it's better than one).
Second, it's easy to go on a run where you lose in the first or second round of several 8-4s in a row. This tends to make for an expensive evening. By playing in Swiss drafts, even though you won't very often come out ahead, it's much easier to break even or just cut your losses.
Finally, I'm more likely to experiment with new or novel strategies in a Swiss draft. I don't want to try out something I'm unfamiliar with in a single-elimination event only to draw poorly and not even have a chance to see how the pieces fit together. Even going 0-3 or 1-2 provides a better learning experience than getting knocked out in the first round without getting to see how things work.
Once I feel comfortable in a format, losing in the first round of an 8-4 stings significantly less. When I'm very familiar with a set, my goals switch from getting some games in and having a good time to winning a lot and proving to myself that I can crush this format. I got there with triple Theros, but I'm nowhere close with Khans of Tarkir yet. So I'll just keep jamming Swiss drafts until I get there. Even though I like the thrill of tough competition, I like playing Magic even more, and Swiss drafts are more likely to provide those opportunities while I'm finding my feet.
What prize structure do you usually play on MTGO? (And please don't say 4-3-2-2. How is that still a thing?)