At the end of the Back to the Future Comic Book issue "Time Served Part 2", when Marty puts the map togehter and then is found by Uncle Joey and Biff, Joey seems to be the intimidating one while Biff seems to be his "nice" 1986 self. In that panel, he's shown taking a drink from his canteen and kinda looking away, as I read Biff's dialogue there I "hear" a dopey nice guy tone. But then comes part 4 and it turns out Biff is the bigger bad guy of the two, with Joey only appearing mean/intimidating to appear to be on Biff's side while Joey only wants to dig up the treasure to return it to Doc. Of course it might not be too surprising seeing as Biff is generally the main villain, but this issue pretty much confirms his "nice guy" attitude towards the McFly's is just an act (unless the hope of getting the money has taken over his way of thinking... after they find that there really is no money, he does go back to acting nice), though it is interesting to see the 1986 version of Biff, who seems to really like Marty, act mean around him and even call him "butthead".
It's fun to think about whether the Biff of 1985 is really nice or if it's just an act when he's dealing with the McFly family (and possibly others). When he sees the Delorean take off in 1985, he does react in a mean tone (which may or may not confirm it), and when he sees Marty, dressed in cowboy gear, he does angrily tell him to get away before seeing that he was rude to Marty. I've seen things that say that Biff thought he was trying to steal the car, but I don't see anything in part III that indicates he thought that (just that he thought he saw a stranger looking at the car polish). The old Biff of 2015 seems to be mean, even badmouthing Marty to who he thinks is Marty's son (though I'd think if he were careful with George's family he'd know better than to badmouth any of them to their descendants), but Biff could have just changed back to being a bit mean by 2015, perhaps it's a case of old age bitterness or the fact that he's still working at his old age and being bullied by his grandson, maybe even both caused him to be that way in 2015. The Biff Tannen in the animated series seems like somewhere between the "nice Biff" and the jerk he was in the real original 1985, though on the animated series George and Lorraine don't appear so he doesn't really have to be nice (though I feel he is a little rude towards Marty here).
At the beginning of the Hard Times storyarc, Marty's sister Linda doesn't seem to like Biff, calling him a lunk, perhaps she sees through his nice attitude or maybe the parents told her about Biff's attempted rape towards Lorraine and, while the parents don't mind employing him despite that, she sees it for the offense it really is.
Also interesting in the last part of Time Served is that Joey tells Marty he learned Biff is a selfish oaf after seeing him as an adult, I assume it means after he got out of jail. But their first meeting after Joey got released shows him no longer wanting anything to do with him already, as if he made his decision before seeing Biff again.
I also wonder about Biff's reaction when he first hears Joey is getting released, which seems like fear but could be excitement. Is Biff afraid of Joey telling everyone that he's the one responsible for his arrest (even though Joey had a code of not snitching on people he commits crimes with/for)? Is he worried that Joey will attack him? Is he excited because now they can get together to find the money?