If you mean guys who punch without putting their hips/legs into the punch then you're asking who was the best puncher utilizing bad technique, which is exactly what arm punching is. In other words it's a rather silly question lol.
Guys like Hagler and Saad were only occasionally arm punchers. Most of the time they got sufficient weight behind their shots and punched relatively correctly. A real consistent arm puncher would be someone like Mate Parlov, Chuck Davey or Calzaghe when he has hand problems.
Davey was a arm puncher, no weight behind his shots in the Galvian fight at all. I am kinda of shock that Davey gave the Kid some problems in the early rounds.
Armpunching can be effective. 1/ Conserves energy 2/ Generally a quicker motion Although there are fairly powerful armpunchers around, I don't know of an instance where amrpunching is actually MORE powerful than putting bodyweight behind the shot. Mayweather comes to mind for being an effective armpuncher, particularly at the higher weights where there is no way he's going to stop his opponents anyway.
Marvin Hagler wasn't usually an arm puncher. He did throw arm punches every now and then, but most of his shots, he would get his whole body into them. Erik Morales and Joe Calzaghe come to mind
In Jin Chi looks like a windmill when he punches. Barely any body movement as he smothers an opponent and he rains down a shitload of hard slapping shots and short hooks and uppercuts.
Pipino Cuevas threw those big loopy punches. He had terrible technique but nonetheless his punches, when they landed, were devastating.
Pernell Whitaker was an arm puncher in every sense of the word. He was always in position to defend. He was an active puncher, and you dont throw shots with your body and leverage behind them without leaving yourself vulnerable. Of course most fighters will at one point in the fight put some leverage in his shot, but for the most part, Pernell arm punched, and quickly brought it back to defend! Winky Wright is another defensive fighter who did the same. Its the reason why they dont have many knockouts.