Deluge is not as user friendly but more powerful than BB, lots of menu diving and scratch head moments, built in synth is ok, fx are a bit lacking. “Unlimited” parts.
BB is very stripped down, like a sketchpad for audio, simple direct, basic, but surprisingly nice features like the sequencer and song mode and quantised launching. 16 parts.
I’ll let you explain OT to him 
I like them all for different things, BB quickest and most limited, OT is most flexible at audio, Deluge is very nice but lacks focus of what it wants to be, IMHO it tries to be all things to all men, however it does have some extremely nice features, polyphonic sample playback, multisampling, looping, but lots of menu diving and a cryptic LCD.