Out of interest to those that have done both which is the more difficult? And do chameleons and bees come close in difficulty?

Bees and chameleons are easy, just time-consuming.

I liked the pond; I hate the topiaries.  Not because they're difficult (they aren't), but because they are repetitive and I find it stressful to have to spot "to order".

I enjoyed the topiaries. But I did the rainbow of fish first, and I was really glad because I used those rainbow rocks for all my topiary unicorns.

The rainbow rocks might have been handy the first time through, but second and after with the same pot it was easy enough to be growing the mushies for the up-coming uni - and the rainbow rocks don't help with the many other rth plants needed. Hardest to work up to a trim was the leopard bush.
Now with the calculator you can plan the mushies instead of having to wait and see .... and possibly get caught out by the regular uni.

I finished the Rainbow of fish after topiary and it was great having rth mushies in the greenhouse, it meant I could get straight on with the next fish without having to wait for the  mushies to grow.
With Rainbow of fish it's only the mushies you have to wait for, with topiary there are usually other stages to do while the mushy is growing.

Not sure about difficulty. I enjoyed the underwater experience and did the rainbow of fish and bottom dwellers together...it made it challenging yet satisfying. The topiaries were monotonous. I enjoyed setting up my garden but the hunting got tedious...and to complete took a long time despite doing several trails at a time excepting the violet which was done solo. The bees were a lot of fun...gambling whether the right colour would show next...but finding the honey blossom seeds can be difficult. The chameleons...can be difficult to spot and there was a lot of competition for them when I did them. I didn't care for them at all...even though I worked with a few friends.

I enjoyed the Pond much more than the Topiaries.  I take my hat off to those that did the TOPs without the rainbow rock but I would recommend doing the pond first & getting the rock first. A lot of UNIs are required. Good luck :)

I've done both and I agree that doing the tops without the rainbow rocks would be difficult.  Everything is time consuming but interesting.  If you have a friend or friends that are doing what you are doing at the same time, it makes it easier and a lot more fun.