ignore the steel vs alu vs carbon nonsense. steel rusts, is hard to find quality steel frames and will be more expensive at this point (for new, used quality steel can still be found if you know what you’re doing. i’m assuming you dont.). aluminum fatigues but for your first bike ridden on easy terrain will last longer than you’ll keep it. alu is the standard these days so is cheap, built strong to compensate for fatigue and is still light. hell, you want longevity, get a quality titanium frame. no rust, bomb proof, tastes great, less filling.