Depends on your research. Is your use case primarily/frequently walking around to various conference rooms, working at a table or in a lab, or are you running intense programs at a dedicated desk? For the first, the 490s and other new thin-and-light laptops are great, for the second, everyone's trying to sell you laptops designed for the first use case, and for the third, a desktop will blow every equally-priced laptop out of the water.
The 's' is the "slim" thinner and lighter version in the T-series. They do use better components (Carbon/magnesium instead of glass-fiber-reinforced nylon) to built the S, and it costs a little more as a result and is easier to tote around. But it will be harder to repair and upgrade than the standard model, and have poorer thermal performance . It also lacks the discrete GPU, has soldered-on RAM vs. the T490's one DIMM slot, and technically lacks an RJ45 Ethernet port.
The T490s does have a proprietary micro-RJ45 port that's thin enough to fit in the laptop and can convert to RJ45 with a special dongle, which to me is the epitome of everything wrong with modern laptops.
GP and I were griping that the T490, like the Macbook Pro, is trending toward the thin-and-light form factor. They dropped the RJ45 port so they could make the T490s 16.7mm thin, and the T490 is 17.9mm thick. My current upgrade plan is aimed at the P53, which is 25.8mm thick, supports 170W of thermal dissipation and processing power instead of 60W, has replaceable/upgradeable RAM, storage, batteries, more ports...and still weighs less than 6 lbs.
That machine can be trivially carried on the brief 2x/day walk from my desk to the lab, and I would't find it worthwhile to cut that weight in half if it means a poorer experience the other 7.9 hours of the day.