Depends on your wind area and your abilities.
These specifications are at best general. One person would manage to get13 gauge in when another would struggle to get 14 in. The 1.7mm is the nearest gauge that an average person should be able to get in there.
If you chose the #13 and managed to get the 73 turns in then it would be the best bet.
Even if you used #13 and were a few turns short then in most cases it would still be the better winding.
If you are in a very low wind area and you can't manage the 73 turns of #13 then the better winding may be with the correct turns of thinner wire but in reality the difference is likely to be slight. Everything is a compromise.
If you are in a high wind area then I would go for #13 and get in as many turns as you can up to 73. If it is a low wind area you may be safer to use the #14 and be sure you can get the 73 turns in.
I trust that you are using the appropriate magnets, Hugh normally specifies metric magnets for mm sized wire and imperial magnets for AWG wire sizes. Changing the magnets does affect the number of turns so be careful.
Flux