I just purchased a Speedo Endurance suit. They're new for 2006 so I can't say if they're any better. The most durable suit is a poly-mesh trainer. They won't fade and barely stretch.

Just get a poly-mesh dragsuit and wear it over your suit.  Two reasons: all suits do in fact fade and wear down; two: poly-mesh suits do NOT wear or fade, and they hide everything very nicely.  Plus they add a SLIGHT amount of resistance so that you're faster when it's race day and you take it off.  Also, always remember to rinse your suit with tap water and ring it out or spin it (if you facility has one) right after you take it off.  Lastly, don't buy suits at retail.  If you wear a drag suit, who cares what design you have?  So look around on the web and in stores for "surplus/grabbag/training" suits that you can normally get for a large discount!