2" deep vs 3" deep???

I prefer 2". My tiers are made up of 1" layers - so a simple split in half does the trick. I also find they bake more evenly. 

UK or USA or Europe or .....(insert name of random country).  Need more information.

IF you are in the USA, then 2" deep is the 'standard' used by nearly all bakeries and home bakers. 

If you are in the UK etc. and will be making fruit cakes, Christmas puddings, etc., then 3" and/or 2" may be 'standard'.