I've used most track barrows around at the moment.
The diesel Slanetrack is head and shoulders above the rest in terms of capacity, power, build quality and noise levels. Things that let it down are its not the most controllable thing even with the revs down, in a tight space its easy to accidently knock the skip into the wall when trying to be gentle turning. Its also the most expensive and as expected for its capacity - quite a wide and large thing down an alleyway. So not for the tightest of jobs but otherwise one hell of a barrow.
The Cormidi's are great little barrows and I used to really rate them, but the C55 I had recently with the Loincin engine was aweful. It struggled to power it, was hard to start and the tip angle of the skip was dreadful even with bone dry shingle. God knows how much would get hooked up if you had wet clay in it.
Shame because the Cormidi used to be the one to beat in terms of size vs capacity - and they were rapid little things too.
I actually bought a JCB HTD5 in the end because value for money - you cant beat it. Diesel engine, electric start, good capacity for its width, tip height is really good and they are one of the cheaper barrows out there. Bad points are they are noisy, turning wasn't good unless you were on a board (the new ones post 2021 have better track motors so hopefully solved this problem) and they are a pain to work on if they go wrong. But I think I'd go JCB again if I was in the market for one. The Slanetrack is a great bit of kit, but no good if it doesn't fit down the side of the house you are working on, and at a third of the cost for the JCB, you can buy a great set of bluetooth ear defenders to wear whilst operating it