do you need an optical out? if you plan to run sound to your receiver then you would need it. do you have a free PCI-E and/or PCI slot? that would also narrow your options. any of the four you choose will do the job though if all you want is a better sound (FYI, better sound card will no improve cheap speakers)
The DX is the best, followed by the DS, Recon3D, and DG. The DG is a special case though, as its the best all around option if you need a powered amp for a headset (<150 Ohms).
As far as the Striker goes, its a good card, but the DX is a slightly newer design. If PCI is a must, you can go either with the ASUS Xonar D1 or HT Omega Striker, as they are basically equivalent. [ASUS offers emulated EAX 5, HT Omega offers DTS Encoding].