i have been in Thessaloniki only, in 1992. Being from Albania, at that time the city impressed me. Downtown area, where that ottoman castle is, was very impressive, modern. Impressive architecture, well regulated and designed streets, to my eyes modern world. Now I have heard are more changes on the seaside, a new promenade but I have not seen it in person. I was working in a village on the hills above Salonica. As we were driving up to the hills the outskirts of the city many irregular buildings were being build, they did not seem to have any apparent planning, and I still wander were they illegaly build or I just got the wrong impression., The traffic was really bad, roads congested, cars parked on the sidewalk. Has it changed? People were helpful and supporters of Micotaki. I was a Papandreu supporter. The climate was a surprise. Even though by the sea, it felt a lot continental climate. I want to visit that city again, this time as tourist with some money to spend.
In short: Downtown area very impressive, can compete with any European city, in developed Europe.
As for Athens, I have heard from other Albanians is generally, beautiful. Parts of it chaotic but worth seen. I definitely want to return to Salonica.