Worth noting that traditionally this spot, roughly, has belonged to Moses for me. However I think it might be time for me to shake up my normal list a bit:
CBarkley 36.7min 22.1pts (.612) 11.7reb 3.9ast 1.5stl 0.8blk 3.1TO
MMalone 34.0min 20.3pts (.569) 12.3reb 1.3ast 0.8stl 1.3blk 3.1TO
Nowitzki 34.9min 21.7pts (.578) 7.8reb 2.5ast 0.8stl 0.9blk 1.7TO
Robinson 34.7min 21.1pts (.583) 10.6reb 2.5ast 1.4stl 3.0blk 2.4TO
CBarkley 11x All Star, 11x All NBA (5/5/1), 1x MVP, 2.437 MVP Shares
MMalone 12x All Star, 8x All NBA (4/4), 3x MVP, 2.851 MVP Shares, 2x All-Defense (1/1)
Nowitzki 13x All Star, 12x All NBA (4/5/3), 1x MVP, 1.809 MVP Shares
Robinson 10x All Star, 10x All NBA (4/2/4), 1x MVP, 3.123 MVP Shares, 1x DPOY, 8x All-Defense (4/4)
CBarkley 1073gms 39330min 23757pts 12546reb 4215ast 1648stl 888blk
MMalone 1455gms 49444min 29580pts 17834reb 1936ast 1199stl 1889blk
Nowitzki 1394gms 48673min 30260pts 10893reb 3496ast 1158stl 1218blk
Robinson 987gms 34271min 20790pts 10497reb 2441ast 1388stl 2954blk
CBarkley 24.6PER, 177.2WS, .216WS/48, 7.4BPM, 93.5VORP, 119ORTG 105DRTG
MMalone 22.0PER, 179.1WS, .174WS/48, 1.7BPM, 46.7VORP, 114ORTG 104DRTG
Nowitzki 22.9PER, 201.3WS, .198WS/48, 3.4BPM, 66.0VORP, 116ORTG 104DRTG
Robinson 26.2PER, 178.7WS, .250WS/48, 7.4BPM, 80.9VORP, 116ORTG 96DRTG
So what I am seeing is this:
On Barkley
I have always felt that Charles Barkley was the most talented PF I've ever seen. Freaky freaky player. Sloppy? Occasionally. But often utterly dominant and could do virtually everything, except defend guys half a foot taller than he was. I don't think nany player that short has ever been so powerful, and no player so powerful has been so mobile. A lethal combination. If you wanted to find a competitor you might have to go all the way to LBJ. Anyway though, it's there in the numbers. Across the board, in the advanced stats, nearly everywhere. He had the 2nd shortest career of the group, and yet aside from point accumulations he beats everybody in everything except blks, and of course Moses' freaky rebounding totals. And needless to say that efficiency is completely freaky. It's the 4th highest number of all time for players who have scored 15,000 or more points (behind Artis, who barely scorer 15k, Dantley and Miller). The other contenders here are all in the same range and Barkley just dusts them. He also dusts Shaq (.584) and Kareem (.596). People pick and choose when to argue efficiency it seems, well as a 6'5" PF Chuck was one of the all time efficiency kings. Which is amazing.
On Moses
My traditional choice for the spot after Dr. J, but after running through all the numbers above, I think I may be ready to move on from that. I've always respected the 3 MVPs, that is a huge factor, or should be. It means that a guy didn't just have a good year, he was considered right up there with the greatest of the great every year for half a decade or more. Every year in the conversation for who 's the #1 guy in the league. But that said, after you get beyond those MVPs, it's just the rebounding and longevity that stand out. Meanwhile he didn't have Admiral's defensive abilities, although people forget once upon a time he made a few All Defense teams, he was a very unwilling passer, and despite an incredibly long career (21 seasons), I am of the opinion, perhaps reflected in the All NBA teams, that his prime was actually shorter than you might think. Perhaps as few as 8-9 years (78-79 to 86-87). No more than 10 really. A peak era of maybe 5. After he left Philly, he hung on a long time without being a big impact player anymore. And then begins to test my conviction that lingering is not a way to truly judge greatness. And given that in most other ways, and certainly once you hit advanced stats, Barkley looks stronger, and my own personal conviction that Barkley was the more talented player...I think I'm ready to make a swap there.
Those are two players I know too, although I was too young to appreciate Moses's true peak, this was the first basketball poster I can remember hanging on my wall:

On Dirk
I am obviously highly uncomfortable when people start trying to inch Dirk up toward the Top 15, but in this neighborhood I think it starts becoming a reasonable conversation. that said, several threads ago I threw out a post about Dirk v. Barkley stating that I needed to be convinced that Dirk > Barkley, and after again laying out all the numbers, that remains true. When you start running through everything, the ONLY real advantage Dirk has is longevity. Even his greatest strengths as a goto scorer and playoff performer are largely neutralized by Chuck being perhaps even better. And efficiency-wise (although Dirk's efficiency does not stand out in this company) people go wild for a couple of Dirk years in particular, his MVP year and the 2011 season. And not surprisingly, those two seasons were the two best efficiency seasons Dirk ever had at .605TS% and .612TS%. Yet that was an AVERAGE year for Chuck. Dirk's longevity really only clearly trumps in raw WS, and raw points. He stands out there, although Moses is close in points. But if Chuck is my standard here, even with all the extra games Chuck STILL piled up more rebounds, more assists, more steals, a huge advantage in VORP and WS/48, and just in general...I think I am going to take a hard look at Dirk v. Moses, but I don't think either guy should be trumping Chuck just for hanging around a long time. Each in their own way was a more limited player.
On Admiral
And if I were going to rank these 4 players on talent, right there with, or possibly just after Chuck would be Admiral. And of course his defense is head and shoulders above the rest of this group too. But here I think the gap in longevity becomes a bit problematic. You can absolutely see in the advanced stats that Admiral is the other really spectacular talent here. But his career was not only the shortest of them all, but he even included a lengthy period at the end where he was playing second fiddle and then functioning as a roleplayer, which blurs a lot of lines when you're trying to figure out how successful and important guys at this level were. We're starting to talk apples and oranges when we talk about Admiral vs. a Dirk for instance, and given the defense I think if he'd remained a #1 player for longer than a mere 7 years that he would be the guy I'd take here. A huge huge talent. As it is, despite the brevity I might be highly inclined to reorder things as:
Erving
Barkley
Admiral
Dirk/Moses
Moses/Dirk
At the very least for this thread I am going to go with:
#16 Erving
#17 Barkley