I think your question is which trading instruments is easier to trade.
There is no particular trading instruments that is easy to trade.
It might be easy to trade (ie also easy to earn $$$) today . Next day it might not.
Let me talk about day trading, trading directional (ie no spreading).
I notice these instruments tend to move in organised manner:
copper, gbpusd, gold, oil, lean hog, live cattle, soya, natural gas, Bund, euro-BTP,
various asian and US indices futures
These instruments are virtually untradable as it hardly move most of the time:
nikkei, corn, wheat, palm oil, at times ES and dax, ZN, GE
These instruments are very violent ie hard to trade:
Heating oil, gasoline.
Important thing is to look at the chart and see how organised, how disorganised / untrendy/messy it is. Also monitor its day range; the bigger the better.