On a road bike, the only components I'd worry about to start are the wheels. Everything else should be sturdy enough to handle around 20 miles a day. If you have very light or low spoke count wheels (say, for 23mm tires, or less than 32 spokes per wheel), they might not hold up to being a daily ride with a load. Fatter tires and more spokes help the wheel carry a load better.

The super-light top of the line components might start to wear out within a year, judging by what I'm seeing from experienced commuters. Midlevel stuff should hold up for years and years with good maintenance. A component that gets used a lot will wear faster than one that doesn't.

If the real issue is hills, poke at the gearing on both bikes. A lot of otherwise sensible bikes have gearing for TdF winners, not normal humans. It's kind of horrifying how many bikes don't have enough low gears. On a cassette, a range of 11-32 or something similar should give you Enough Low with a triple in front. Sheldon Brown's gear calculator is a lot of fun for this.