Very interesting thread. As is the answer with many questions in this hobby... it depends.
In general larger tanks are easier for novice reefers basically for the simple reason that bad things happen slower. A simple nano could be setup and maintained by an experienced reefer with little time and effort, however if the nano becomes more complex with more delicate organisms nanos can quickly become more difficult than larger tanks.
There is a difference between more difficult and more time consuming. The larger the tank the longer a water change takes, but that has nothing to do with difficulty.
I say these things because I've went through so much with my 10 gallon over the past year and a half that has challenged and taught me more than any of my larger tanks ever have. My tank has been referenced in this thread and others, so I'll bump up the major thread for reference. In September I got a larger system going, and have recently moved some of the stony corals out of my nano because I was running into unavoidable issues with this amount of calcifying organisms in such a small amount of water.
The issues were these. The nano was originally started using only small additions of B-ionic and water changes for replenishment. I then gained confidence and began carefully dripping kalk nightly, starting with a dilute solution and working up to full strength. I then went to the point where I needed B-Ionic on top of the kalk. This progressively got to the point where I was dosing 25 mLs a day of B-ionic in my 10 gallon on top of the kalkwasser. The problem is that the alkalinity buffers (part 1 of B-ionic) cause a spike in pH, which isn't much of a concern in larger tanks, but in my nano it was. General knowledge is that a sudden change of up to .2 in pH is acceptable (ex. 8.2 to 8.4). With the addition of between 3 and 5 mLs of part 1 I would get a spike of about .2. So, in summary, I was doing about 6 additions of B-ionic daily on my system, 2 in the morning a half hour apart, 2 after work, and 2 at night. Then there was the problem of the B-ionic increasing my specific gravity over the course of just a day or two, resulting in my water changes being made with dilute IO. This was tough enough for me to handle, but when I travel for work the instructions left behind to my wife and retired father were getting ridiculous.
That was a bit of a ramble, but the point is that smaller tanks could be much more difficult to care for, but if done simply they could be less time consuming. My calcium and alkalinity levels were always in need of adjustment due to the small water volume and high uptake.
It is however a great challenge to keep STABILITY, which is what many of these organisms thrive on, especially those like sps and clams. At the same time if kept healthy they are very resilient in the event of short term disasters, of which I've had many. Forgotten kalk drips where the pH went up to 8.9, power outages where the pH dropped to 7.5 with a temp in the low 70s, and many others... we've come a long way in this hobby...
lastly I'll say that with nanos the rewards are greater :happy: , but the setbacks are more