So the way I see it is:
KILL TREVOR - This is the 'middle' option, sort of OK if you will. He's clearly a maniac and not a very happy one at that, and you could make the case for putting him down. I still didn't feel at all happy about doing it though - (it didn't seem to pan out too well for Franklin either as the post mortem texts and phone calls make it clear the murder has isolated him, and the FIB simply cut him loose) - there was no way I was going to let that be my 'proper' save going forward to 100% completion - so it was onto....
KILL MICHAEL - This is definitely the 'bad' ending, I would have never done this except to see what happens, and true enough it was pretty horrible, I really felt sorry for Michael (and Franklin!). Even after the initial confrontation and chase, when you get him dangling over the edge of the parapet, it doesn't actually matter if you drop Michael or pull him up, if you pull him up he lands a headbutt on you and drops to his death anyway.
Quite a powerful ending this one, and in the aftermath Trevor disowns Franklin, Amanda says she hopes he rots in hell, Jimmy tells him to get fucked, Lamar keeps his distance, and so on. (If you go back to his safehouse and go to save the game but immediately back out, it winds time forward on six hours, so you can see/hear all the emails/messages/phone calls that follow on from the murder.)
'DEATH WISH' (Kill neither) - I see this as the 'good' ending. I'd decided in advance this was going to be for my 'proper' save so dived in despite the lateness of the hour made a start on it, not expecting it to be quite so involved...
Turns out to be one of the longest and arguably the hardest missions in the game!
After Lester and Franklin's initial despair at the situation, Lester comes up with an idea to get the FIB and Merryweather together at the foundry. Thus commences a massive shootout featuring all three main characters and Lamar, but it gives Michael and Trevor a chance if not exactly to 'bond', at least to be a bit more on the same wavelength.
Following on from that it's loose ends to clear up, so you have to kill Cheng, Baines and Stretch - and then it's onto Devin at his armoured fortress in the hills. One more shootout and a kidnapping later, and you push him into the sea in the boot of his car - cue a final scene where the three characters agree to be flawed friends.
I was much happier with this ending so will indeed use this timeline to push through to 100% completion. Each character is sat on between $42M and $50M, and I still have three Lester assassination missions (which I've deliberately left) to do so will be able to properly clean up on the stock market and basically buy everything on the map