I started off with a dual breed (good layer, but meaty enough to eat if the need arose) - Buff Orpingtons. For me personally, they were so-so on the laying, did NOT mix well with any other breed, and they eat, ALOT. I'm gradually switching over to Black Austrolorps. It's a personal preference. Lots of people go with the Cornish X when they decide they want meat, and stick with a good laying breed for their eggs. I haven't tried the X's, but my MIL did. Out of 25 birds, she wound up with 4 survivors. I like options with my flock
I agree with the comments on the BOs and the BAs. 100% on the BOs...not good feed conversion, not good laying for the long term, not hardy, too docile for free range and poor foragers. The old time, heritage line BOs were a different breed of cat but the BOs one can obtain nowadays are largely pet quality and not impressive for laying or meat economics.
My personal all time favorite dual purpose bird is the White Rock...there really are no down sides to this breed and they are hands down the heaviest breed that still lays up to par. No other breed can touch them IME. Regal, hardy, good mothers, good flocking instincts on free range, great foragers, excellent feed conversion, longevity of lay, great rate of lay, calm and approachable but aloof, even temperament, wonderful feathering and molt recovery...whatever good you can say about a chicken, it applies to this breed.
Second and an equally great bird, though not one to lay on a lot of meat and lacking in the sheer
presence of the White Rock, is the Black Australorp. Great laying, longevity of lay, friendly, quirky, hardy, goes broody on occasion but not too often and my hands on favorite for sheer laying for years on end without getting laying issues like a RIR or Leghorn will. They just don't burn out, these birds. They forage great, have good feathering and molt recovery, good flocking instincts and wariness on free range.
If I could only choose two breeds to have in this world, these two would be my top picks.