What is the best bike saddle to reduce pelvic pain?

First, make sure you get the right size saddle to fit your sit bones... Many saddles will come in 130mm width or 145mm width. 

If your unsure your sit bone width, get fitted at a local bike shop. However, if you want to try and figure out your sit bone width yourself, you can try the following:

1) Take a piece of tin foil (large enough to sit on)
2) Place the tin foil down, at the top step of a staircase that has plush carpeting.
3) Sit down on the tin foil, then take your feet off the ground to put a little extra pressure on the tin foil.
4) Measure at the center, between the two indents in the tin foil to determine your sit bone distance.
5) Add 10 to 15 mm to your measurement to get the proper saddle width.

Once you know your proper saddle width, you'll then want to find a saddle that has a proper cutout to reduce pressure on your perineum.

The first saddle that receives high marks from many riders for reducing pelvic pain and pressure is the Selle Italia SLR Superflow saddle (or the Selle Italia SLR Gel Flow Max saddle). The Selle Italia SLR Superflow saddle is a light weight, flat saddle, that comes in 131mm or 145mm and has one of the largest cutouts of any bike seat.  The Superflow saddle can be a pretty hard seat for mountain biking if you're not use to riding on a dense seat, so you'll definitely want to wear padded chamois for long rides, but the more you ride the more comfortable it will get. You may find the best price on Selle Italia saddles at ChainReactionCycles.com

Alternatively, you may want to try the Selle SMP Hybrid saddle which has a lot of curves and padding.