If you plan to use the pistol as a carry gun, I would recommend no safety since you don't want to have to deal with disengaging the safety during a stressful event. Just get a good holster that protects the trigger and you will be all set.
If your primary use will be a range gun, then you may want to consider the safety. I have one on my Ruger SR9c, and I will often engage it before letting others with me shoot it just in case they accidentally get careless when initially picking up the firearm.
Having said that, I just picked up a new Shield 45, and specifically ordered it without the safety.