After an artificial swarm, the queen cell i left to grow, was a dud, I had chosen the best looking QC and it was already capped....I am now leaving the hive to produce another queen, does anyone have any good advice as to how to chose a good queen cell, when the time comes
You got unlucky.
The conventional wisdom is by picking an open cell you know the larva is ok and also a better handle on when the queen should emerge.
The conventional wisdom is also a well sculpted surface is better than a smooth or unsculpted surface. Not totally convinced of that myself.
The choice of cell is often described in rather absolute terms, when in reality you may have a less obvious choice to make. Sometimes it’s more about actually which ones you don’t choose. I prefer not to choose bent cells, cells drawn in restricted circumstances, outlying positions or disproportionately long or short.
However they are preferences assuming their is an option remaining which is still ok.
If there is a risk of going queenless I strongly prefer making two separate colonies (maybe a nuc) rather than leaving two cells.