Honestly, unless you really want a Glock, I don't see any advantage the Glock has over the M&P. The M&P is a bit less blocky, and it has ambidextrous slide stop. The Glock has right-hand-only slide stop. Also, unless you get a Gen4 Glock, you are limited to right-hand only mag release (instead of reversible) and there are no interchangeable backstraps pre-gen4. Those might not matter to you, but as a lefty with small hands, these features certainly matter to me. On the M&P you also have the option of a manual safety.
Caracal offers 18 rounds in flush magazine (+1 compared to G19/M&P), XDm offers 19 rounds, both come with ambidextrous mag release. I don't really remember the stats on the XD, but XD/XDm have a grip safety, which some like, some hate - I'm ambivalent towards.
There's also the Ruger SR series, but I haven't looked too much into it as it only comes with a manual safety, something I don't like. They have the longest butt of the slide compared with the other striker-fired options, but they are cheap and a lot of people like them. The last options are a Taurus 24/7 or FN FNS, both which have a lot of ambi controls, but come with manual safety.
Pretty much all of these striker-fired options are nice. As you can tell, as a lefty, ambi controls are very important to me, which is why I'm listing those in the description. How it fits in your hand is also important. Of all the ones I mentioned, XDm or M&P is likely what I'd go with. In fact, I'm still not sure between those which one I want.