I think any Gaggia will work just fine. From what I've read pretty much all Gaggia machines use the same internal parts, just different materials externally. Of course something that's wrapped in stainless will be higher than plastic, but both work the same. Main interest in the Gaggias is the well built grouphead and portafilter. Only problem most complain about is the aluminum boilers used in them. IMO it doesn't matter what type of metal alloys are used for something like this. All will eventually corrode to an extent. Just use high quality softened water in your machine, descale it often and you'll be fine. Later!
BTW, before I bought a decent machine I used a DeLonghi steam machine (which uses an aluminum boiler) for at least 7 years. I used softened, balanced (proper PH) water and cleaned it every month or 2 and the internal parts looked like new when I gave it away. It all comes down to how you take care for something.