What would be your preferred ammunition for carrying a S&W shield in the woods?

I'm very unlikely to be attacked by anything. I'm in PA, so unless I kick a bear cub I'll be fine. Still..

Instinct tells me Buffalo Bore heavy lead 9mm, but I feel I'd lose most of that velocity with the short barrel.

HST 124 gr. Look at shootingthebull's video on youtube.
If you're worried about bears I would just carry a spare mag of FMJ honestly in a 3" barrel.

HST or Gold Dot. I like 124s since that's what I have but I believe 147 HST is the gold standard right now and especially out of a shorter barrel.

From that short of a barrel, I'd use FMJ.

My preference is 147 HST in mine, but I have 124 +P Gold Dot, too.

I think Buffalo Bore hardcast you brought up is a good idea. Remember the bullet does not expand, so it is okay that it will be going slower … it will still penetrate a lot. I’d consider recoil and how well it cycles but assuming it works well in your gun I think it’s likely the best option.

Another good choice IMO is the Lehigh Defense Penetrator bullet (115gr Xtreme penetrator loaded by Underwood as well). There is some marketing bs about the flutes doing damage, but the shape of the bullet keeps it forward-oriented to penetrate deeply and I think the hard bullet would be more consistent in penetrating the skull of a large animal. This bullet would be much more pleasant to shoot than the buffalo bore.

Personally in that small platform I'd probably go with the lehigh bullet but both are good options. You could also look into the cost of bear spray and just get some.

I'm more worried about humans than animals.

Go with your carry ammo.

Same here. Not too worried about wildlife in PA

Fed HST 147
Winchester Defend 147
Gold Dot 147
all standard pressure.

I've typically gone with hardcast for 9mm and .40S&W woods carry.  Biggest four-legged threats are only black bear and wild hogs.  

Another option I've been strongly considering based on my own observations is Lehigh's Xtreme penetrator ammo.  A solid copper bullet with great penetration and so far, pretty reliable results in gel (I've only tested watermelons) with significant permanent wound cavities.

For me, I typically do distance backpacking, so weight is a concern.  I usually just pack my Kahr CM9, which is a short barreled 9mm to boot.  The high velocity appeals to me as with the ballistic gel results; however, the penetration of a solid (although a lighter grain) appeals to when considering heavier skin, muscle mass, and bone.  I usually don't buy into exotic ammo designs, but after doing some research and seeing that Black Hills has done significant testing, I'm pretty comfortable giving this a serious consideration to meet my requirements.

I'm really liking this option for now and will continue to test...

ROCK6

I load my own 165 fmj 9mm for my suppressor so I think that would take care of any thing.