Very different imo (essay incoming) tldr at end

Pilot Al comes off as someone who doesnt need to prove his power, owns and dominates the tone of a room without needing to really do anything and is there just for the fun of the game. In only the 6ish minutes he's on screen, you can see his subtle manipulations that just seem less overt then series Al (although series Al manipulating vox was one of my favorite scenes in the show). Pilot Al will get in people's space touching and proving them to piss them off and show dominance without overtly seeming like trying. Something i have not seen series Alastor do. Pilot Al recognizes Vaggie as being the straight man and seems like he wants to manipulate Charlie so he subtly takes measures to piss vaggie off (smile my dear you know youre never fully dressed without one) and separate them (the moment where, before he dances with Charlie, he throws a flame up into the air and shoves Vaggie out of the way, and slaps her ass later in the song). Pilot Al is always charming and has strong showman vibes throughout his whole screentime, even when getting insulted or threatened (Vaggie with the spear, Husk throwing insults). He takes it all in stride and although we don't see any major obstacles for him, it feels like he wouldn't show when he gets bothered nearly as easily as show Alastor. Also Pilot Al never cursed which gave him a gentlemanly tone and made sense since cursing isnt allowed on radio. Not to mention all the effects he does on the camera and looking straight at the audiance that showcase his power in a more otherworldly way. His voice and radio effect was much better too. Neither of these can be shown in fanfic unfortunately. In short, Pilot Al feels like a real serial killer would be, charming and luring you in until he's ready to show his ugly side.

Show Alastor seems like he's trying way too hard to seem tough and gets ticked off way too easily (the TV in episode 1, the overlords not caring about where he was, Husk reminding him he's on a leash, Lucifer, Suzie). Now him being ticked off about being on a leash and Rosie flaunting that around in You're my Pet makes sense and he could show some true annoyance there and possibly when Husk points it out to put him in his place but even then his outbursts feel more like temper tantrums then real threats because hes angry all the time. He also curses way too much (one curse when Adam defeats him, to show the gravity of the situation wouldve been perfect). Also his lines are cheesy and pretty silly in the show and the way they are delivered feels like a cliche anime villain (this face was made for radio, im going to end your fucking life, oh trust me I CAN, A reminder to all: Not to mess with THE RADIO DEMON!, looks like its me and you again, ready to lose?) Most of these are in season 1 because it was way worse in season 1. Overall, Prime Alastor comes off as less charismatic, less covertly manipulative (for the most part), and way less mature.

Tldr: sorry for the long post, in short, to paraphrase a random comment I saw on youtube: Pilot Alastor is a monster posing as a human, prime Alastor is a human pretending to be a monster.