Not controversial, because he was awesome...Controversial opinion I know, but as someone who grew up closely watching all three, and saw them live many times, I honestly think Plugger was the best of them all, and the best player I have seen in my lifetime following footy (since 1986)
Plugger had a more significant and profound and longer lasting legacy on the game (especially in a pioneer state in Sydney) and his all time goal scoring record will never be broken (least in my time)
Annoys me that Lockett is rarely discussed in the GOAT of the game status, in my opinion he is comfortably in the top 5, if not 3, of the VFL/AFL history.
As some have stated though, the categories need to be split...
You can't safely define the world's best ever guitarist, for example - Hendrix often wins the polls, but there are dozens of players across different styles who are technically better in that style, or who contributed more in their genre...no doubting his influence, but does that make him a better actual player? Imagine him without an acid tablet in his headband. Then you get on YouTube and find nobodies who can beat all the greats...!
Lockett was the icing that made Sydney an actual footy team, and his record probably won't be broken unless they throw in rules that skew the game in favour of goal kicking. Coaches and observers all say that his skill set was utterly elite, even if he wasn't the most mobile player - he could never kick a goal on the run like Franklin did that day twice v Essendon, but you knew he wouldn't miss from 50...well, he did once, but it still got the Swans into the GF...!
For me, it's Carey, but Ablett, other Ablett, Daicos (younger people, he invented that s**t, and if you youtube him you'll see what I'm on about), Baldock, Matthews, anyone named Bunton...too many to fit into 5...just like Hendrix, Davey504 (speaking of youtube), Van Halen, Vai, Davey504, Gibbke, Davey504, Malmsteen...Davey504...