What kind / model handheld radios do y'all recommend? Looking to talk in semi-mountainous terrain but have no idea where to begin w/ radios...

I have used many of the hand held radios from Midland and Motorola. I have yet to get even close to the range they advertise. Short range they work pretty good but if you get more than a couple miles out especially in hilly terrain they don't work that well.

The basics are HF (high frequency), VHF (very high frequency), UHF (ultra high frequency); HF propagates the best in the hills for unlicensed hand held units, a better chance of getting bounce or skip, though the power output is usually low, 4 watts. All may have problems, VHF may work better in the woods because it penetrates better, but won't penetrate a mountain or bounce or skip. The longer the antenna the better a radio will work in the hills, which causes issues with a hand held. All of the advertised distances for hand held units are under optimal conditions.
HF can have a lot of radio traffic. Many of the VHF and UHF units are more private.

I have a HF unit that has a 500 watt booster and there are canyons around that kill the signal. One in particular, that must be iron ore, that is basically a total dead spot.

Your conundrum has been around as long as radio has. I wouldn't count on any to work flawlessly in all terrain.
A story about this; I came across a guy who had rolled his Jeep and broken his back in the mountains. I radio'd out and got an answer 50 miles away, bounce/skip. Tried to get a helicopter, but they weren't sending one on my say so. Finally sent my brother out in a high speed buggy. He came back hours later with an ambulance that had traveled ten miles of bucking bronco dirt road to get there. I didn't stick around for the climax, I sure hope they didn't try to drive this poor guy out in that ambulance. There was the tallest mountain around between me and the guy I'd raised on the radio. I could talk to him but to nobody closer. Radio waves can be unpredictable.

Great information from Mudderchuck. You will likely receive even more information by calling Motorola or another manufacturer directly.

It has been a while since I used radios. I used both Midland and Motorola. I remember calling Motorola for advice. Ended up using their recommendation and was pleased.