1 hive is the best
I rarely make a definitive statement like that.
One needs to be sure that their arguments stand up to total scrutiny.
There is not a 'best'. I never tell anyone they must buy two colonies, I just recommend that course, as do many others.
I wonder how many queens have been lost in one way or another by an over-enthusiastic beginner. As beginners we all want to check the colonies to gain experience as quickly as possible often before the nuc expands into a full colony. Bad news. Too many inspections and inexperienced operatives.
The cost of two hives and colonies need not be much more than one hive, two colonies and a couple of extra queens. Lets face it you need hive tool, smoker, spare bits and pieces and a beesuit whether one or two or more colonies. I always liked the beek who kept telling people it only cost 50 quid to start beekeeeping - a scond hand hive, a swarm and a net curtain, and a lot of luck, I daresay.
I was going to start with two full colonies but was mentored by a very experienced beekeeper who, unfortunately, was giving up his two colonies due to ill health, so I started with four full colonies. Two Nationals and two WBCs. Gone up and down in numbers since then, including zero.
I didn't realise what pussy-cat bees were until I collected a swarm one summer. Later I met a fellow who was a starter with two colonies. One had died out over winter, the other was so docile (Bromley beekeepers, thumbs up!). He had only 50% losses that winter and something to go forward with, for a crop and recovery to two colonies.
I know that nucs and queens are much in demand this last couple of years. Two reasons - first, winter losses and secondly the renewed interest in keeping bees. They will increase again next year, I expect.
One could be spending over £600 to start with one nuc in a hive. I started with 4 for not much more than half that amount. I would not like to count up how much my hobby has cost over the years. I just enjoy it and the Association meetings, etc. Personally, I would not want to spend a grand to start with two colonies. Most need not, if they go about it in a sensible way. Ymmv.
Regards, RAB