I have the following machines in three different homes: QM Silvano, QM67, and Gaggia New Coffee (ca. 1989). In all three I have Sette 270, and in 2 of them I have Fresh Roast 500.
The most important equalizer is the Sette 270 in all locations. I previously used a Braun KMM30 with the Gaggia, and the shots were poor.
I am very happy with the Silvano. Although not E61, it is 58 mm and therefore the portafilters, baskets, levelers, tampers are interchangeable with the QM67. In comparing the Silvano with the QM67:
1. It is lighter
2. The water chamber slides out from the side vs from the top(QM67). This could be important if you mount it under kitchen cabinets.
3. It does not have a hot water spout.
4. Both have timers for the shots.
5. I believe the Silvano cannot be plumbed, whereas the QM67 can.
6. The QM67 uses a double boiler, the Silvano has a thermoblock for steam output.
7. The Silvano steam is enabled with the flick of a switch, the QM 67 has a multi-turn valve. The valve may have a "bling" factor, but flicking a switch is a lot easier, especially when the milk is rapidly getting too hot.
8. In terms of milk frothing I am equally not expert in both of these machines. I do not see much difference.I recommend you purchase the Isomac New 2 Hole tip for $10 from Chris Coffee. The 2 holes are smaller than typical, thus compensating for possible lower steam pressure.
I do not have personal experience with the Breville Double Boiler, but from what I can read, it is a very sophisticated impressive machine. It has all sorts of parameters you can play with such as adjusting preinfusion. It is not built as solidly as the Silvano, but Breville is good at servicing the machine.
I think the Silvano is a very solidly built machine which has, to some extent, the "look" of the more expensive Italian machines. It is very user oriented and, with a good grinder, will make excellent espressos/caps. It is a tremendous value for the money.
If you enjoy experimenting with various parameters, and have the skill of noticing subtle differences in the cup (I don't) you might prefer the Breville.
You could not make a mistake with either machine. Buying both of them is a great idea!