While there are important differences between marketing automation platforms, success is often primarily determined by three things: your strategy and process, your content and lead flow, and your people. With limited investment in these areas, you can usually get good (but not great) ROI from marketing automation. But the more you invest, the higher you move up the curve, and the better your return on investment.
The key is to think big, start small, and move quickly. In other words, the best results usually come from getting started with what you have today and then incrementally investing over time.