Hey, glad you beated it! :)
Endings are grouped in three major groups: A - when you spare all your victims, B -when you kill all of them, and C - when you killed at least one and spared at least one. Blaster Cop difficulty makes them a bit better, and/or fuller, and there also are other few minor factors for some changes. I personally think that the best ending you can get is when you doing it on hard, with a 'C' ending.
>payment can't be processed
Ah, yes, always having some problems with this paypal synchronization, I'm thinking I should just remove that 'name your price' stuff, cause it doesn't work for me here, anyway. Also, if you are still interested to support, you could try my patreon for one month, or something like that, https://www.patreon.com/arkhidexx
You also can see there my current project's posts, about Archtower game.