I have experience with some of these bikes, though earlier model years where the equipment was a bit different. My dad has a 2015 DS4 and I have a 2015 Verve 3. Both of these have Suntour suspension forks with preload adjustment; only the DS has a manual lockout. I bought my particular bike without having ever ridden anything with suspension, and I probably won’t go back to rigid, at least not for my primary bike. It’s THAT comfortable to me. I ride probably 50-60% paved trails and probably 40-50% dirt/gravel two track. Even if I rode 100% on the road, I’d still take the suspension. Look, I’m 235 pounds (and dropping!); the one pound I save with a rigid fork is FAR outweighed (literally) by my weight and that of my clothes, gear, etc, and is also FAR outweighed by the increase in rider comfort -- for me. That is certainly a personal choice, though.

I like the DS series bikes, but do you also have the option in your buying program of the DS2? The DS2 is going to net you some significant advantages, including an 8-speed cassette freehub and Acera derailleur. The DS1 comes only with a 7-speed freewheel and an Altus rear derailleur. There is a $110 difference in MSRP between the DS1 and DS2, but I think it’s very worth it to step up.

At that ~$650 price point (of the DS2) is the Verve 3. Unlike my 2015 model, the current ones don’t have suspension forks and, instead, use wider 45-622 tires to aid in comfort. In exchange, you’re getting a 9-speed Alivio drivetrain on the Verve 3 for the same price as the 8-speed Acera on the DS2. Whether or not you want to trade suspension for an extra rear cog is up to you. Of course, the bikes have different geometry as well, so I highly advise you go ride them all in any event. The Verve series does use an adjustable quill stem, which I generally prefer over the threadless stem on many modern bikes, including the others in your lineup. They’re not as easily adjusted as something with a quill stem.

I don’t have experience with the other two Treks on your list, though I know the FX is highly respected. I don’t know much about the Marlin series.

To your comment that you like the DS’s front suspension and you like the Verve’s wider tires, my dad has 29x2.1” tires on his 2015 DS4. They just BARELY fit, and they’d be too tight for me. But the point is, you should be able to easily fit the 45-622 tire size on a DS bike. The Verve’s tires are smooth-tread Bontrager H5s, anyway, which would not be appropriate for much “trail riding” – you’d probably want to buy new tires in either situation. Your Trek dealer might offer to swap tires for you to something else they can order. In that case, you might have a pretty good choice of a number of different brands, depending on what, exactly, they sell.

Good luck!