As regards depreciation, if one had bought a new Auris in the past few months and were looking to change it now, then depreciation may be an issue. However, as yours is 3 years old any effect due to the replacement will be minimal, if noticeable at all.
The other cars mentioned have been on sale for longer than the Corolla, so the finance incentives may well be more attractive as the period of initial demand has passed.
The other cars also have a shorter new car warranty.
As regards VED, the same will apply to any car bought from April 2017.
Really only you can decide whether your best move would be to wait, sell your existing car privately or part exchange, use a car buying website or whatever. Yes, some people will advise to sell privately, but that can involve a fair degree of time and hassle. Can you afford to be without a car should there be a gap between selling your car and getting the new one.
You need to do some investigation as to what is best for you rather than rely on advice which may not be fully au fait with your situation.