Given the OP specifically stated 40SW as one preferred option and an attraction to M&P, gave no indication of intended purpose and feels he has smaller hands, and given I own (and shoot) two M&Ps one of which is chambered in 40SW...that seems like a recommendation with some basis to me. Also given my hands are 'average' (based on an actual but informal internet survey of hand measurements of about 500 guitar players) and that 'several people'
have mentioned they find the M&P pistols easy to operate and more comfortable than other popular guns, it seems like a solid recommendation.
Like many handguns available these days, it's as easy to use left- or right-handed, and as I regularly shoot all my handguns weak hand only, that's based on my personal experience.
I also own one Kahr (K40) and wouldn't recommend that for a novice shooter necessarily--it's extremely small IMO, and a very special shooting challenge. Single-stacks aside, I find no size advantage to 9mm over 40, and certainly would never select a single stack gun just because my hands were on the small side. I find tiny little 9mm auto pistols as miserable to shoot as any gun available, and simply wouldn't recommend one to anyone classifying themselves as 'a novice'.
Not a caliber war here by my account, for sure, and not a LOT to go on beyond the usual 'what should I buy next?' thread. But, I think folks are generally responding well to what was provided.
Maybe a good recommendation is to find a public or private range that rents--I know some clubs have a fairly-wide selection to choose from for rentals and that can really make a difference.
Range toy, target shooting, backwoods plinking, concealed carry, home defense/nightstand gun, vehicle gun, shooting a lot or just from time-to-time, plan to handload or no, plan to customize with drop in parts or remain pure stock, preferred price range? All of these can drive 'better' choices or recommendations--