I'm using Blutak - mainly because I need the speakers as low as possible (the gel pads add a good half inch to the height). I had a limitd height within which to place my M&K S150's in order for my screen to drop below the window (to block out more light). As it was, Atacama specially made me some shorter HMS2's to fit the bill.
The Nexus aren't good enough for the SCM11's. They're one of the heaviest standmounts below the £1k mark, and need a very sturdy stand to get the best from them. Most of our customers have opted for one of the Partington models, but the HMS2's will also do a great job.
A speaker has to be as still as possible. When the bass cone, particularly on long throw drivers like the ATC's, are forcing themselves forwards, it's natural for the cabinet to be forced backwards. If the cabinet can move backwards, the bass cone doesn't have a solid patform to move forward from, 'blurring' the effect and intention of that cone movement. A similar effect can be likened to using a pair of speaker stands with lose fitting spikes. Generally, single column stands aren't rigid enough, and tend to be a style choice. Two columns is much more rigid, but only along the horizontal plane of the two columns, three columns is far more stable, but I'd recommend four columns for maximum rigidity. The top plate and base plate also have their part to play. The base plate needs to be large - the larger the base plate, the larger the footprint, therefore the more stable the stand. The more of the cabinet the top plate supports, the more secure the speaker that sits on it. Filling the columns with heavy material gives a lower centre of gravity, making the whole structure more stable, although too much raises this centre of gravity, and can also have a detrimental effect on the overall sound.
Stands welded together tend to be more rigid, but most stands tend to be flatpacked nowadays for ease of storage at manufacturer and retailer, and also smaller packaging for easier shipping. The better Partington stands are all welded.