I have an older generation (corded) Fein Multi-Master. It's an excellent tool. I've used others and there is no comparison with respect to vibration and power. However and this a big however, I find that I use it FAR less than I anticipated. When needed, it's handy, but I just don't seem to need it very often. Of course, that's just me and my work. Fein and others sell a lot of these tools so there must be a lot of folks whose work is elevated and/or streamlined with an oscillating multi-tool. Carry on.
I used the DeWalt that the church has (I do volunteer work there on Mondays) some more. In addition to tool less blade changes, it has speed control via the trigger. I will soon have a Milwaukee M12 increasing me to 4 of these tools so I don't need another but that DeWalt is a nice tool.
The fein cuts better than the other two I currently have (HF and Ryobi cordless) because the stroke side to side is about twice as large. Whatever tool you use, it is really nice to have some carbide blades for cutting metal. They last a LOT longer than bimetallic. I have both Bosch and Milwaukee and they cut about the same. A set of assorted blades is a good way to start out and the Bosch set comes with a nice storage case (Milwaukee's is not as nice but still useful).
I too have the corded Rockwell Sonicrafter. It was gift from a friend. I borrowed it to help with some flooring and trim work and got to keep it. Never had one before and now there are some things I wonder how I got by without one. Nothing to compare it to, but the tool less blade change is simple. It takes a variety of common blade configurations, so finding the right blade is easy as well. If I was to buy one, both of those features would be a must. Would also opt for cordless.
Pretty sure he is regretting letting it go. I'll be glad to let him borrow it any time though.
I have a couple of these, a Ryobi 18v and a corded FastCraft that I got at Costco. Both work well for what they are designed to do. I started with the Harbor Freight model, then went to Sonicrafter before settling on my current tools.
Blades make more of a difference with these tools than with any other tool I have. I get mine from here and here, and have been very happy with both. In a pinch, Bosch blades from Home Depot are good.