There is no best cruise to suit everyone. You need to give more details about your needs & wants. Do you want party party, peace & quiet, the best food, formal, informal, the most exotic itinerary, the cheapest, the dearest, the noisiest, classical music, karaoke, the list is endless........Wilba .
I agree with everything that Wilba has said and would also add that I have cruised several times by myself and far prefer this type of holiday to a land based holiday on my own. So as Wilba says, give us more of an idea what you like and we will be able to make many suggestions.
I agree with the others. It really depends how old you are too.
It is also worth considering which ships have single cabins. You can be lucky booking a double cabin for single occupancy but on popular cruises you may pay well over the odds. Several companies including Fred. Olsen and SAGA have single cabins on their cruise ships.