Heavily loaded bicycle
You will get a lot of opinions but like many above I'm for reliability and durability. Your bicycle is hauling groceries which is a very unforgiving load plus you on there pedaling the hole thing down the road. Try to make a list of all the rim brands, number and size of spokes on all the failed wheels and don't buy them again. When hauling dead weight loads you are going to need much stronger wheels than even us Clydes normally run. At minimum I would run 36 spokes. One can get 13/14 gauge spokes. But you have been breaking 14 gauge spokes at the rim so the next realistic size is 12 gauge spokes or more 14 gauge spokes as in 40 or 48 hole wheels. 12 gauge spokes are readily available from electric bicycle shops and will be much stronger than 14 gauge. Worksman Industrial bicycles use 10 gauge spokes. I have a Worksman Cycle Truck that carries the load in a front basket. The wheels have never groaned under even full grocery store runs. Some people would say this is way overkill and thumb their noses at the very idea but I love that bicycle for its everyday reliability and durability for hauling things. If you use 12 gauge spokes the hubs and rims will need to be drilled out a little to fit the bigger spokes. This is not a hard job to do. The rims really need to be strong as in Velocity Chukkars or the like. I see several rims listed in previous reply's as equivalent to the Chukkar. My experience is with the Chukkar. Take your pick. There may be a bicycle garage or co-op in your area that will teach you how to build your wheels. If you have the time that would be a lot of fun learning and your wheel build will be as good as any out there. Good luck