I made a bit of a mess initially because I went with steam thinking it was the right choice, then I found out it really depends on how you manage things at home. In my case, with bottles and pacifiers multiplying everywhere, steam saved my life - I sterilize in the evening and have everything ready in the morning. But I know people who sorted it out perfectly well with Milton for a third of the cost, it depends if you have the space and patience to organize yourself with soaking.
What bothers me most about steam is that it uses more electricity and makes noise, which at 6 in the morning isn't great if the little one is still sleeping. With cold sterilization instead you do the mix the evening before, throw everything you need in there and forget about it. But obviously, you need at least half an hour for the solution to work.
One thing though - other people say steam degrades the pieces faster, and it's true that after a few months of daily sterilizations the valves start to get damaged. If you're thinking of using it for a long time, cold sterilization is actually less harsh on the materials. As for marketing, steam isn't a pointless gimmick, but it's not indispensable like the ads make it seem, if you have the discipline to do the soaking. What would you do if you had to manage the bottles: are you more of a wing-it type or do you prefer to plan things?