System-Ex, Zenith and Ambrosio are the same, I think On-One are something different but similar quality. I have a Ambrosio, it's nowt special, cartridge bearings which don't last long for winter riding. I'd prefer traditional cup and cones with proper seals though, but at this price point they don't exist. I think the ones you mention are good VFM though, don't get me wrong, one needs to pay more for better stuff.
I'd go for the Spa wheel set or if I could buy the parts more cheaply build them myself. I'd choose these simply because I know more about the components and On-One leave a bad taste in my mouth and Spa are jolly nice people to whom I don't mind giving my money.
The Mygal chainset looks OK, as does the other one you linked to. Some cheap Stronglight stuff is a bit soft though and doesn't last as long as one would like. The rings on many chainsets tend to be cheap and need replacing sooner than one would like. Rogerzilla had a Sugino for sale which might suit you. A Sugino RD is another alternative to look at, you'll often find some on eBay for about £50.