Hi, mosy. I think folks generally are happier with Shimano hydraulic brakes -- at least from the standpoint that pretty much all Shimano hydraulic brakes are good. There are, of course, performance tiers as you go up in price, but there really aren't any poor performers. I've had the Tektro brakes that come on the 2019 Roams, and I don't think they're bad brakes, but they are a step down from the Shimanos. They use the same size pads, so you can interchange them, and upgrade the Tektros with any performance pad that's available for the Shimanos. But the Tektros, I think, do not have brake lever reach adjustment (and the Shimanos do). You can't adjust the free stroke with either one, but you can at least set the free position of the lever on the Shimano brakes. I also like the bleeding design on the Shimano brakes better, which have a separate bleed screw and bleed port. The Tekros use a combined bleed screw/port and it's not quite as clean this way in my experience. My dad has a 2015 Trek 8.4 DS with the Tektro brakes, and one of the calipers started leaking at the seam, so he replaced them with Shimano Deore brakes.
Having said that, I personally recommend paying more attention to other aspects of the bike, like the fit, frame style, color choice, etc. You can buy a pre-bled set of the Shimano brakes for $50-70 on eBay and install them yourself. And that's one nice thing about the Roam over the DS, in my opinion: the shift cables and rear brake hose are routed external to the frame (vs. internal), which makes maintenance and replacement a snap. They all route down the downtube under the smartly-designed downtube protection on the Roam, which is another nice plus: you won't get stone or gravel chips in your downtube paint. But anyway, you can easily swap to Shimano brakes eventually if you want them (or right away) with the Roam.
If you like the Roam better, I wouldn't let the brakes stop you from buying the bike. The Trek is over $150 more expensive for essentially the same set of components. The drivetrain is near identical. The fork is identical. They both have 38mm tires. If you add the cost of replacing the brakes on the Roam, you're still $75-100 ahead of the Trek. I've owned a number of Treks, and still have four, but I bought my 2018 Roam 2 because I just couldn't see spending more on the DS.
Another option: it looks like there's still some 2018 Roam 2 stock kicking around, at least according to
Giant's website. See if they have the size and color that interests you in a bike shop near you. I bought the Satin Grey, and I really like the color.