I would say you are ok with either one, but I personally have Faulk listed higher on my board. I think the Rams have one of the best offensive lines in football and according to the website Fanball.com Pace is expected to accept a one year offer from the Rams within the next week.
Warner is back and looks good, and I think that will help Faulk out immensely. On the other hand, Alexander for the most part has been injury free and the main advantage he has is that St. Louis, San Fran, and Arizona all have weaker run defenses than Seattle so he may put up better numbers than Faulk against teams within the division.
If it was me, I would go Faulk though (unless something happens and Pace doesn't sign)