I like modified Kanban boards, both when startup is in reactive mode, and as an alternate view of a really good Gantt model when I'm doing serious planning for less-reactive hitting of deadlines and synchronization points.
But if I were an agency doing hourly billing of clients who didn't know what they wanted, I would like Scrum. "C'mon, give us a straight answer to our questions, we're locking you into that for another 300 billable hours. Then you can pull other answers out of your behind in a week. We'll call it participatory design, or interactive, or something, and pretend it's that it's because this is the most efficient way to solve hard problems, or to be flexible at the superfast speed of business. But really it's because you are bad at what you do, and just pretending, so we decided you'll pay my firm 300 uninterrupted billable hours per week as your penance. I'm thinking of scaling up my team, so that we can bill-- uh, execute, faster."
But if I were an agency doing hourly billing of clients who didn't know what they wanted, I would like Scrum. "C'mon, give us a straight answer to our questions, we're locking you into that for another 300 billable hours. Then you can pull other answers out of your behind in a week. We'll call it participatory design, or interactive, or something, and pretend it's that it's because this is the most efficient way to solve hard problems, or to be flexible at the superfast speed of business. But really it's because you are bad at what you do, and just pretending, so we decided you'll pay my firm 300 uninterrupted billable hours per week as your penance. I'm thinking of scaling up my team, so that we can bill-- uh, execute, faster."