The Delaware, Dorking, Heritage New Hampshire, Heritage Plymouth Rock are breeds that I would consider.
If you already have Sussex then you are about set it they are from a well breed utility line.
I had Black Copper Marans and Basque Hens for my Dual Purpose breeds. I liked the Marans better. They out laid my Basque hens, and were larger fuller birds too.
I am now down to just keeping Cream Legbars. They are a laying breed but we still use them for meat.
If you are looking for a meat bird that is a true dual purpose bird the Sussex it is. I recommend the Delaware because ti was the #1 commercial meat bird in the US before the cornish crosses took over the industry and if you are looking for a meat bird that can lay well they are a top choice. I recommend the Dorking because they were breed to have soft meat even in older birds and spent layers. That always appealed to me because our meat comes from culls and may of those culls are retired flock members rather than 16 weeks old surplus cockerels. The New Hampshires and Plymouth like the Sussex are both well round dual purpose birds. It really just depends on who you get them from as to what quality they will be. If you get any of the dual purpose breeds from a person that had paid close attention to growrates, mature weights, and utilities you will be happy. If you get the same breed from some one that doesn't measure and work at improving utilities you probably won't be happy.