Asus get reccomended by a few magazines, but they get working motherboards hand delivered and dont have to fix the problems with them thats left to us, and weve had alot of people with problems with Asus boards.
ATI are the complete opposite in Europe they are at least a good $150USD cheaper than the Nvidias which as well as being faster is a big incentive as to why i like them. ATI are going market to market establishing a base at the moment they are concentrating there effirts in Europe it will be North America or Australasia next so you might get lucky in the next couple of years. Its not all to much difference if ones cheaper than the other go with that ATI are better but the differences arent huge the x1800XL and the 7800GTX are pretty equal on most fronts now with the 6.1 catalysts out.
You could wait for DX10 or you could get your system now, but you could always get your system now and stick a 6800GS in it and wait for DX10 flog the 6800GS when it comes out and get a good DX10 card. You have to make that decision yourself.
The MSI board comes in SLI(Diamond version) but unless you are going to do SLI from the start i wouldnt really bother unless there is something else you want thats in the SLI boards. The MSI boards have one of the highest levels of build quality so they are good on that front and the price is good as well(You also cant beat the nifty red CMOS button, why no one thought of that before i will never know). Also core cell is good they are probablt the best all rounder boards good at a bit of everything really.
On the DFI the extra PCI-e x16 slot is essentially redundant you cant really use it with two gfx cards it was just a way to save money on the boards so they dont have to make SLI and non SLI. They are among the best boards for overclockers if you have good enough cooling to handle them at the high clocks.