The variants of Giulia sedans are many, similar overall, and very confusing, especially from a nomenclature aspect. Check out
Berlina Register and click on the Giulia discussion to get a primer. There's lots more info on the web about it. My own take from best to least-best (no such thing as "worst" Alfa sedan), listing models realistically to be found in the US. This assumes decent, stock condition, but they call all be modified pretty easily for a lot more performance. And finding a good one of some of these can be quite tough.
* Giulia Super
* 1750 Berlina
* 2000 Berlina
* Giulia TI
* Early Alfetta sedan
* Late Alfetta sedan
* Milano
* 164
You're not likely run into a Giulia TI Super, Giulietta TI, 2600 Berlina, Alfa Sei, or other exotic, so I've stuck with what might actually come up on the BB, ebay, or CL. Just my two cents with two seconds of thought put into it. Others will feel differently.
Andrew