DoomAttack is faster on my BlizzPPC 040/25. faster then 68k ver of adoom that is and ya get all the other extras the doomattack provides such as freelook.
To get best speed out of it, youll have to mess with the gfx plugins and see which best suits ya system, its far better then adoom in my opinion.
Addom pretty much keeps to the original dooom.doom2 game, adds nothing more but tries to stay completely compatable with all doom stuff. Doomattack started adding wonderful extras that gave a reason to actually fire up the ole game again.
As for RTGMaster, i dont remember it requiring it, as the game used its own blitter gfx plugins, but maybe there was options to utilise rtgmaster instead, i cant remember.