I'm agonizing over this decision. Leaning toward Nik right now, seems more refined, would appreciate feedback from anyone who has gone through the same, which one you chose and why. Use LR more than Photoshop but will purchase the full version of one of their suites.
I own both suites. They tend to have strengths in different areas. For ME, the most used applications in the OnOne suite are PhotoTools and PhotoFrame. But, I use Alien Skin's Bokeh instead of FocalPoint (which is good). In the NIK Suite, I tend to use Viveza and Color EFX Pro. I used to use DFine more before LR3 and ACR CS5. You need to try the demo versions of the suites and try and figure out which applications you will use and which you won't. FWIW, I find PhotoTools more useful in actual images than Color EFX Pro.
Most, if not all of the functions that exist in the suites can be done with plain Photoshop ... with enough expertise. So if you are troubled by the cost, you might want to invest in Photoshop education on lynda.com as a reasonable lower cost option. I'm not against the suites and use them constantly because they are so fast and produce nice results. One advantage is that they allow you to quickly explore a number of creative options.