I have to disagree ever so slightly on the dyson's performance. In my honest opinion, the felix and dyson are very much neck and neck. They both win, in the own way, if this makes sense.
I love the dysons agitation. The suction at the head is the best I have ever come across on a vacuum. The agitation is very good. However, I have found on very low pile carpeting (I have kitchen carpet in the, yeah, kitchen!) it doesn't do as well, as the head is elevated slightly with the tiny wheels on the head. I think the bristles could do with being fuller and maybe two rows, and longer. What I most dislike about the dyson is probably the massive brush motor belt thing which leaves and inch of carpet ungroomed, and although I overlap my strokes, it is not a clean sweep. It means when you over lap, you have to make sure you go over the bit which is missed.
The felix on the other hand still has very good suction, even at the cleaner head, although it isn't as well sealed, which is a good and bad thing. It doesn't snow plough at all, and although you can change the slider on the dyson, when you do this, you loose a lot of suction.
The felix is much simpler in design, which a lot will like, in terms of how it performs. It is a large brushroll, thick with long stiff bristles, 2 rows and there are a lot of bristles.
With the sebo, you obviously do get a decrease in suction as the bag fills, but it is nothing on the scale bagged vacuum used to be with paper bags.
And as sebo_fan said, we are vacuum enthusiasts and not the average consumer. We love vacuums, not just one particular brand. Dyson and Sebo are my favourites for their respected type (bagged and bagless)
I have disregarded modern day Candy Hoover, Morphy Richards, Russell Hobbs, Samsung and Vax to producing cheap, throw away vacuums. I find Hoovers to be very over priced for what they are. Vax typically are well priced. None of these manfuacturers make "original" genuine vacs, rather produced by a third party somewhere in China. With dyson, Sebo, Numatic and Miele you are buying in house designed and made vacuums. Thing is, some hoover and vax products are as expensive as mieles and sebo's, but you are buying Chinese quality, not German or British quality.