Hi and welcome.
Gen 1 to Gen 2, minor changes, wheel size is 0.5 inch wider (more common tyre size) and all the rest is cosmetic and computer control changes.
Do you like the older look or the bonnet postbox look?
You'll find that a Gen 1 has more age-related issues than the Gen 2. Engines are the same so what's starting to go on one, will start to go on another. Saying that, engine problems are few. Biggest gripes are engine mounts wearing prematurely (relatively cheap mod that many people have done), road noise (common in the wheelbase used for the mazda, focus and volvo) and in my case (Gen 1) some tie-rod end knocking that is a design issue. No biggie, just when you drive over bumps you get a slight clunk over time. Each service, I get them to tighten the bejeezus out of them (been told that's what you have to do) when on a rail-hoist (needs weight on the wheels to truly be tightened).
Depending on your tastes, more integrated functionality (Bluetooth etc) in the Gen 2, Gen 1 gets an Aux point in the centre console, but that's it.
Watch for smoke. Take a car for a test drive from cold. Start it up and let it idle for 5+ minutes, see if it smokes. Give it a drive, a few good hard jabs on the accelerator, etc etc, get it hot then let it idle after the run. If you get smoke in any of the situations (not just on hard acceleration, that's just the rich running of the car), turbo seals could be gone/going. Some people have this issue and need to replace them.
Otherwise, they are a relatively strong and reliable car. Great daily driver and fun when you want to go for a squirt through some winding roads. Don't expect to be dragging people off at lights etc, they are quick, but unless you drive like a lunatic you won't be winning any awards. Definitely more fun for winding roads.
Best of luck finding your future fun car!
3 MPS - Rolling on Pirelli PZero Neros, sitting on Bilstein B12's, stock internals... still makes me smile with the Zoom Zoom.