What trim is the 2017, loaded could mean xlt 202, limited, kr or platty? Towing would be the least of your issues, both tow the same amount very well as long as you have the tow pkg. The 2019 will have a higher payload capacity though. I owned a 2009 nav and 2018 expy limited without ccd, But have driven a 2017 expy with and without ccd so here are my thoughts.
2017 pros and cons:
Pros - reliability(projected) less items to break and the 6sp is bulletproof, ride comfort (ccd) if you get a platty, more usable cargo room(boxy design makes it easier to use cargo space), price, load leveling option
Cons - handling is a bit loose/soft, ride without ccd wont be as good as 2019 without ccd, not as much passenger space or comfort, empty fuel economy(not towing, fe is nowhere near as good), interior design, feature content severly lacking, condensation issue with eb
2019 pros and cons:
Pros - ride comfort, better handling, better fuel economy empty, a lot more passenger space, way more feature content(xlt 202a with tow pkg will give you adaptive cruise, lane keep, collision detect, and convenience features without opt for less reliable features), reliabilty(if you stick with xlt, the 2018 ltd i owned had gremlins but was mostly bulletproof).
Cons - leaky shocks(biggest issue with 4th gen without ccd), tow fuel economy, design hampers rear cargo(more space behind third row, but the cargo entrance and area is narrower by comparison), price and availability(tow pkg 4th gens are unicorns), no load leveling opt, cam phaser issue on eb
Id research the different forum threads here because there are plenty of user experiences and data for both 3rd and 4th gen trucks. I personally enjoyed my expy more than my nav, but do wish i got a platty or expy or navy instead of the ltd i ended up with. Both will meet your towing need, so Drive both and see which you personally enjoy more. However if you budget is about 45k, go look for 2020 xlt on discount, ppl on the 4th gen thread are seeing 12k+ savings on new trucks. That way youd get a new truck thats now reliable(noone in their 2020s are rele complaining about problems), with new warranty and way more available with what you personally are wanting in your truck.