If you're new to handguns then I would definitely NOT recommend either of the choices you suggested, here's why. Little guns are more difficult to shoot accurately than full sized ones, especially for people just starting out. And they are, IMO, less fun to shoot. Their small size and weight makes it difficult to get a proper grip and does little to help control recoil.
I'm 5'6 and 150 lbs and carry either a Glock 23 or 5" 1911 on a daily basis. The 1911 prints almost none if I wear a medium sized t-shirt and the Glock doesn't print at all. Since you're looking at 9mm I'm going to recommend the Glock 19, it is a VERY easy gun to shoot, it is easily concealable, and offers respectable capacity for a 9mm handgun. You will enjoy shooting it more and be more inclined to practice and hone your skills. If one day you decide you need something smaller the pocket 9s are always there.
One thing to consider before you buy a Glock, and you have to be honest with yourself, is how diligent are you about practicing gun safety? Glocks are NOT forgiving about gun safety mistakes. I always do my utmost to be muzzle and trigger conscious but I am always just a hair more so when handling a striker fired gun without a manual safety such as a Glock, like finger extended as far as possible from the trigger guard conscious. Probably overkill but that's just me.
If you HAVE to have one of the two you mentioned and are not open to suggestions then I would have to say the shield simply because it's bigger.