Francis Ford Coppola or Martin Scorsese?

It depends how you view artists "at their best who was the best" or "longer, sustained" - I view them the first way, and that's Coppola over any American ever.

Hard to compare considering I've only seen 4 Coppola movies while I've seen 14 Scorsese movies. I'll go with Scorsese for now tho.

These are in my top 100:

1. Taxi Driver- 10
2. The Last Temptation of Christ- 9
3. Apocalypse Now- 9
4. Raging Bull- 9
5. The Godfather- 9
6. The Godfather: Part II- 9

I would say Coppola just gave everything he had all at once, and after a point just relaxed into the 80s, then tried to back in the early 90s with The Godfather: Part III and Dracula.  Didn't happen; and then wasn't able to materialize into something substantial after that, and people just stopped caring about him.

Scorsese....  Of course he was one of the original boys of the American new wave.  But I actually think that Altman and Coppola were originally considered the American new wave innovators (they had more acclaimed films in the 70s than Scorsese did) and Scorsese was probably peripheral and wasn't thought of as a master yet..... until probably Raging Bull.  He would have good stuff after that of course, but I think Goodfellas is the turning point into his more commercial/entertainment side, and Cape Fear/Casino are movies that define the later day brash and non-subtle Scorsese, and that trend continued all the way to today.   There are films in his post-90s period that are better than others, but I don't see all that much of a change in style as to what the latter day Scorsese became as soon as Goodfellas came out.  I still enjoy how he's able to continuously entertain me, even though I realize it's sometimes via cheap, rehashed, and non-subtle methods, to me that still gives him at least that - and it's an extra good thing, for me personally.

Scorsese ! My all time favourite director

Scorsese, though it is pretty marginal if we compare their ultimatum magnum opus (Taxi Driver, Apocalypse Now), but Marty just doesn't get anything wrong (Raging Bull came close, but even it has some glares to justify its status today)

it's Coppola. Even though, I wasn't wild about Rumble Fish, The Godfather trilogy, The Conversation, Apocalypse Now, and the severely underrated One from the Heart, Finian's Rainbow, Tucker: The Man and His Dream, and Peggy Sue Got Married, push it in his favor.

I might be wrong but as far as I know ..... One from the Heart lost so much money he had take "jobs" from the studios for the next decade-plus because he was in debt. Having said that I think he made great films after '81.  Rumble Fish is brilliant. Tucker & GIII are underrated. Dracula, a lot of inspired mad-genius directing there. Then comes the dip. Jack is career-low. Rainmaker solid if middling. Big gap where he abandons his epic Megalopolis. Then he returns with a new "film student mentality" - his words - with the weird flawed failures Youth Without Youth & Twixt, but does Tetro in the middle which shows he's still a strong writer/filmmaker. Now he's bothering with what he calls "Live Cinema" - like it's some kinda new miracle. "It'll take me five years." Meanwhile Woody Harrelson did it btwn joints. He should return to Megaloplis - which would strike hot in this political climate.  

Summation: it isn't just downhill after One from the Heart. 

Scorsese by far.

Scorsese, Coppola had an excellent peak in the 70's, but after Apocalypse One, he sorta went off the deep end and become a director for hire, he made some good films, but he never had that high peak, unlike Scorsese who has proven to be one of the few directors who still makes constantly good / great films, even in his old age.

Well, it isn't so much to me that people like different things with him though as its people identified themselves as Scorsese fans post-Goodfellas and rewarded his films (good or bad) by turning out consistently for a few years in its aftermath, very deep into his career. No one in the general audiences much cared that he hadn't won an Oscar prior to Goodfellas, afterwards it was de rigeur to chant it to anyone who would listen. Prior to that film people didn't link him by name with his films as much as they did post-Goodfellas and that film crystallized who he was in a pop culture sense.

Casino was over 40 million, Cape Fear near 80 million, Goodfellas near 50 million, 32 million (not shabby at all) for The Age of Innocence - he was drawing audiences in this period like he never had at all consistently and repeatedly. 

Well I know he didn't win but Goodfellas started his commercial era. Goodfellas-Casino, 4 films in a row are more interesting to look at than 2 films that are 6 years apart like Color of Money and Cape Fear, right?

It was because Goodfellas through Casino were films that put ticket buyers in seats expressly because of his name which got established on Goodfellas and again it was deep into his career when that happened. I don't think the audience seeing Color Of Money knew his name at all honestly in '86.

I do get what you're saying that those are his 2 biggest pre-DiCaprio hits and that's a fact, but that doesn't really tell a deeper story that to me anyway is there to tell (in my OP).