Gold / OWS is the most useful if you travel frequently on OW airlines as that gives you lounge access / priority check in and boarding on other OW carriers too. Free seat selection is also included for many OW carriers.

Also, you don't get penalty for cancelling an award flight if you are Gold or Platinum - useful if you need the flexibility. Gold / Platinum also used to get 5% Avios discount for award ticket, but they've removed this benefit.

Chasing for Platinum is probably not worth it for most travellers as the gain is marginal, while first class lounges and fast track security are also not available in many airports.