I find Eureka to be dwarfed by Empress & Spectre
Size wise, Empress & Spectre are similar.
Only issue for me is Spectre's weapons. They are way too thin for my taste, even with their excuse that they are "true scale"
I find Empress minis to be a bit too "static" ( yess I know they are toys ...
), compared to Spectre's who are designed with a stance more dynamic.
I also mix with Assault Group minis. their design is a bit dated now, but I like them and to my (tired) eyes, they are ok.
Empress and Spectre's vehicules and stuff mix well. I also ordered from Anthenocity Workshop, who produce nice 1:50 pick ups and other motor vehicules, as well as street furnitures, all in great quality, and readiliy available ...
Hope it helps
Fred