In principle CE is always worth the extra Avios due to the large amount of extra personal space at your side.

However I identify two exceptions:

i) if you are travelling in a family with small children as a group of three or six. In this case there is no practical advantage over ET as the small child can sit in the middle of the 3-3 in ET

ii) the extra Avios spent on CE would cause you to lose out on a CW trip or UUA to CW in the future.